Manufacturing method of semiconductor device

ABSTRACT

The invention provides a technique to manufacture a highly reliable semiconductor device and a display device at high yield. As an exposure mask, an exposure mask provided with a diffraction grating pattern or an auxiliary pattern formed of a semi-transmissive film with a light intensity reducing function is used. With such an exposure mask, various light exposures can be more accurately controlled, which enables a resist to be processed into a more accurate shape. Therefore, when such a mask layer is used, the conductive film and the insulating film can be processed in the same step into different shapes in accordance with desired performances. As a result, thin film transistors with different characteristics, wires in different sizes and shapes, and the like can be manufactured without increasing the number of steps.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/986,243, filed Jan. 7, 2011, now allowed, which is a continuation ofU.S. application Ser. No. 11/458,266, filed Jul. 18, 2006, now U.S. Pat.No. 7,867,791, which claims the benefit of a foreign priorityapplication filed in Japan as Serial No. 2005-221983 on Jul. 29, 2005,all of which are incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a semiconductor device and a manufacturingmethod of a semiconductor device.

2. Description of the Related Art

A thin film transistor used for a semiconductor device, a displaydevice, or the like is required to have different characteristicsdepending on the purpose or function of the semiconductor device. It isimportant to control the characteristics of the thin film transistor tosatisfy the requirement, and a technique for manufacturing the thin filmtransistor has been researched to provide characteristics appropriatefor the intended use.

In a thin film transistor, by etching a gate electrode layer intostacked layers of different shapes or a tapered shape and addingimpurity elements by utilizing the etched shape, a technique to formimpurity regions with different concentrations in a semiconductor layerin a self-aligned manner has been reported (for example, see PatentDocument 1).

Patent Document 1

-   Japanese Patent Laid-open No. 2002-203862

However, when a shape of a gate electrode is controlled by etching asdescribed above, there is a problem in that a wire, a capacitorelectrode, and the like formed in the same step result in having similartapered shapes to the gate electrode.

SUMMARY OF THE INVENTION

The invention provides a technique which enables manufacturing of asemiconductor device and a display device having high resolution andhigh reliability at high yield without complicating the steps andapparatuses.

It is to be noted in this specification that a semiconductor devicecorresponds to a device which can function by utilizing semiconductorcharacteristics. By using the invention, a multi-layer wiring layer or asemiconductor device such as an IC chip can be manufactured.

Moreover, by using the invention, a display device can be alsomanufactured. A display device applicable to the invention includes alight emitting display device in which a thin film transistor(hereinafter also referred to as a TFT) and a light emitting elementformed of electrodes sandwiching a layer containing an organicsubstance, an inorganic substance or a mixture of an organic substanceand an inorganic substance, each of which exhibits light emission calledelectroluminescence (hereinafter also referred to as EL), are connected,a liquid crystal display device which uses a liquid crystal elementcontaining a liquid crystal material as a display element, and the like.

According to a manufacturing method of a semiconductor device of theinvention, a first semiconductor layer and a second semiconductor layerare formed; a gate insulating layer is formed over the firstsemiconductor layer and the second semiconductor layer; a firstconductive film is formed over the gate insulating layer; a secondconductive film is formed over the first conductive film; a first masklayer over the first semiconductor layer and a second mask layer overthe second semiconductor layer are formed over the second conductivefilm by using a light exposure mask which transmits light at a pluralityof intensities; the first conductive film and the second conductive filmare etched by using the first mask layer and the second mask layer; afirst gate electrode layer and a second gate electrode layer are formedusing the first mask layer, and a third gate electrode layer and afourth gate electrode layer are formed by the second mask layer; animpurity element imparting one conductivity type is added to the firstsemiconductor layer by using the first gate electrode layer and thesecond gate electrode layer as masks and to the second semiconductorlayer by using the third gate electrode layer and the fourth gateelectrode layer as masks, thereby a first high concentration impurityregion and a first low concentration impurity region which overlaps thefirst gate electrode layer are formed in the first semiconductor layerand a second high concentration impurity region and a second lowconcentration impurity region which overlaps the third gate electrodelayer are formed in the second semiconductor layer; a third mask layeris formed over the second semiconductor layer, the third gate electrodelayer, and the fourth gate electrode layer; and a region which overlapsthe first low concentration impurity region in the first gate electrodelayer is removed by using the third mask layer and the second gateelectrode layer as masks.

According to a manufacturing method of a semiconductor device of theinvention, a first semiconductor layer, a second semiconductor layer,and a third semiconductor layer are formed; a gate insulating layer isformed over the first semiconductor layer, the second semiconductorlayer, and the third semiconductor layer: a first conductive film isformed over the gate insulating layer; a second conductive film isformed over the first conductive film; a first mask layer over the firstsemiconductor layer and a second mask layer over the secondsemiconductor layer, and a third mask over the third semiconductor layerare formed over the second conductive film by using a light exposuremask which transmits light at a plurality of intensities; the firstconductive film and the second conductive film are etched by using thefirst mask layer, the second mask layer, and the third mask layer; afirst gate electrode layer and a second gate electrode layer are formedby the first mask layer, a third gate electrode layer and a fourth gateelectrode layer are formed by the second mask layer, and a fifth gateelectrode layer and a sixth gate electrode layer are formed by the thirdmask layer; a fourth mask layer is formed over the third semiconductorlayer, the fifth gate electrode layer, and the sixth gate electrodelayer; an impurity element imparting n-type conductivity is added to thefirst semiconductor layer by using the fourth mask layer, the first gateelectrode layer, and the second gate electrode layer as masks and to thesecond semiconductor layer by using the fourth mask layer, the thirdgate electrode layer and the fourth gate electrode layer as masks,thereby a first n-type high concentration impurity region and a firstn-type low concentration impurity region which overlaps the first gateelectrode layer are formed in the first semiconductor layer, and asecond n-type high concentration impurity region and a second n-type lowconcentration impurity region which overlaps the third gate electrodelayer are formed in the second semiconductor layer; a fifth mask layeris formed over the first semiconductor layer, the second semiconductorlayer, the first gate electrode layer, the second gate electrode layer,the third gate electrode layer, and the fourth gate electrode layer; animpurity element imparting p-type conductivity is added to the thirdsemiconductor layer by using the fifth mask layer, the fifth gateelectrode layer, and the sixth gate electrode layer as masks, thereby ap-type impurity region is formed in the third semiconductor layer; asixth mask layer is formed over the first semiconductor layer, the thirdsemiconductor layer, the first gate electrode layer, the second gateelectrode layer the fifth gate electrode layer and the sixth gateelectrode layer; and a region which overlaps the second lowconcentration impurity region in the third gate electrode layer isremoved by using the sixth mask layer and the fourth gate electrodelayer as masks.

In the aforementioned structure, as the exposure mask which transmitslight at a plurality of intensities, a semi-transmissive film (alsocalled a semi-transparent film) which reduces the intensity of light topass through or a diffraction grating pattern having a non-opening andan opening with a width of the resolution of the exposure apparatus(resolution limit) or narrower may be used.

By using the invention, a highly reliable semiconductor device anddisplay device can be manufactured through simplified steps. Therefore,a semiconductor device and a display device with high resolution andhigh performance can be manufactured at low cost and high yield.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A to 1D are views showing manufacturing steps of a semiconductordevice of the invention.

FIGS. 2A to 2F are views showing manufacturing steps of a semiconductordevice of the invention.

FIGS. 3A to 3E are views showing manufacturing steps of a semiconductordevice of the invention.

FIGS. 4A to 4F are views showing manufacturing steps of a semiconductordevice of the invention.

FIGS. 5A to 5D are views showing a manufacturing method of a displaydevice of the invention.

FIGS. 6A and 6B are views showing a manufacturing method of a displaydevice of the invention.

FIGS. 7A to 7C are views showing a manufacturing method of a displaydevice of the invention.

FIGS. 8A and 8B are views showing a manufacturing method of a displaydevice of the invention.

FIGS. 9A and 9B are views showing a manufacturing method of a displaydevice of the invention.

FIGS. 10A and 10B are views showing a display device of the invention.

FIGS. 11A and 11B are views showing a manufacturing method of a displaydevice of the invention.

FIG. 12 is a view showing a display device of the invention.

FIG. 13 is a view showing a display device of the invention.

FIG. 14 is a view showing a display device of the invention.

FIG. 15 is a view showing a display device of the invention.

FIG. 16 is a view showing a display device of the invention.

FIGS. 17A and 17B are views showing a display device of the invention.

FIGS. 18A to 18D are views showing structures of a light emittingelement applicable to the invention.

FIGS. 19A and 19B are views showing manufacturing steps of asemiconductor device of the invention.

FIGS. 20A to 20C are top plan views of a display device of theinvention.

FIGS. 21A and 21B are top plan views of a display device of theinvention.

FIG. 22 is an equivalent circuit diagram of a display device shown inFIG. 23.

FIG. 23 is a view showing a display device of the invention.

FIG. 24 is a view showing a drop filling method applicable to theinvention.

FIG. 25 is a view showing an electronic device to which the invention isapplied.

FIG. 26 is a view showing an electronic device to which the invention isapplied.

FIGS. 27A and 27B are views showing electronic devices to which theinvention is applied.

FIGS. 28A and 28B are views showing application examples of asemiconductor device of the invention.

FIG. 29 is a diagram showing an application example of a semiconductordevice of the invention.

FIGS. 30A to 30G are views showing application examples of asemiconductor device of the invention.

FIGS. 31A and 31B are views showing application examples of asemiconductor device of the invention.

FIGS. 32A to 32D are views showing electronic devices to which theinvention is applied.

FIG. 33 is a view showing a display device of the invention.

FIGS. 34A to 34C are views showing structures of a light emittingelement applicable to the invention.

FIGS. 35A to 35C are views showing structures of a light emittingelement applicable to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiment modes of the invention are described in details withreference to the drawings. Although the present invention will be fullydescribed by way of embodiment modes with reference to the accompanyingdrawings, it is to be understood that various changes and modificationswill be apparent to those skilled in the art. Therefore, unless suchchanges and modifications depart from the scope of the invention, theyshould be construed as being included therein. Note that identicalportions in embodiment modes are denoted by the same reference numeralsand descriptions thereof are not repeated.

Embodiment Mode 1

A manufacturing method of a thin film transistor of this embodiment modeis described in details with reference to FIGS. 1A to 1D. It is to benoted that one thin film transistor is described in this embodimentmode; however, it is needless to say that a plurality of thin filmtransistors can be formed at the same time on the same substrate.

An insulating layer 301 is formed as a base film over a substrate 300and a semiconductor layer 302 is formed over the insulating layer 301.In this embodiment mode, a crystalline semiconductor layer is used asthe semiconductor layer 302. A gate insulating layer 303 is formed overthe semiconductor layer 302 and a first conductive film 304 and a secondconductive film 305 are stacked thereover. In this embodiment mode, agate electrode layer formed over the gate insulating layer is formed tohave a stacked-layer structure; therefore, the first conductive film 304and the second conductive film 305 are stacked. The semiconductor layer302 may be doped with a slight amount of impurity element (boron orphosphorus) for controlling a threshold voltage of a thin filmtransistor.

A mask layer 306 is formed for etching the first conductive film 304 andthe second conductive film 305 into desired shapes (see FIG. 1A). Themask layer 306 is a resist pattern formed by etching a resist into adesired shape by an exposure mask. The exposure mask used in thisembodiment mode is an exposure mask provided with a diffraction gratingpattern or an auxiliary pattern formed of a semi-transmissive film witha light intensity reducing function. The diffraction grating pattern isa pattern provided with at least one opening pattern such as a slit or adot. When a plurality of openings are provided, the openings may bearranged regularly (periodically) in some order or randomly(non-periodically). By using a fine diffraction grating pattern havingan opening with a width of the resolution of an exposure apparatus ornarrower and a non-opening, a substantial amount of light exposure canbe changed, a thickness of an exposed resist film after development canbe controlled, and the resist can be processed into a more preciseshape. Therefore, by using such a mask layer, a conductive film and aninsulating film can be processed into different shapes in accordancewith a desired performance in the same step. As a result, differentkinds of thin film transistors, wires in different sizes, and the likecan be manufactured without increasing the number of steps.

The first conductive film 304 and the second conductive film 305 areetched by using the mask layer 306; thereby the first gate electrodelayer 307 and the second gate electrode layer 308 are formed (see FIG.1B). The shapes of the first gate electrode layer 307 and the secondgate electrode layer 308 reflect the shape of the mask layer 306. Inthis embodiment mode, a width of the first gate electrode layer 307 iswider than a width of the second gate electrode layer 308, and the firstgate electrode layer 307 extends to exist outside the side edge portionsof the second gate electrode 308. By the etching step for forming thegate electrode layer, the gate insulating layer is partially etched(also called film reduction) and becomes thin in some cases. Therefore,in this embodiment mode, by the etching step of the first conductivefilm 304 and the second conductive film 305, the gate insulating layer303 of a region which is not covered with the first gate electrode layer307 or the second gate electrode layer 308 is partially etched and has aless thickness. For the etching, dry etching, wet etching, or the likecan be used. It is to be noted that the mask layer 306 is also etched inthe step of etching the first conductive film and the second conductivefilm; thereby a mask layer 309 is formed.

Moreover, the first conductive film 304 and the second conductive film305 can be etched into desired shapes to form wiring layers in the samestep as the step of forming the first gate electrode layer 307 and thesecond gate electrode layer 308. In this case, by using a mask formed ofan exposure mask provided with an auxiliary pattern having a lightintensity reduction function such as the mask layer 306 for a wiringlayer as well, a wiring layer having a shape which is freely set inaccordance with a position or a function can be formed. In order toimprove the coverage of an insulating layer or the like to be stackedover the wiring layer, the wiring layer can be formed so as to have astep (or a tapered shape) at edge portions similarly to the first gateelectrode layer 307 and the second gate electrode layer 308.Alternatively, the wiring layer can be formed by precisely stacking afirst wiring layer and a second wiring layer with approximately the samewidths. When the stacked layers have the same widths, wiring capacitancebetween the stacked layers is reduced.

By introducing an impurity element imparting one conductivity type tothe semiconductor layer 302, an impurity region is formed. In thisembodiment mode, an impurity element imparting n-type conductivity (inthis embodiment mode, phosphorus (P)) is used as the impurity elementimparting one conductivity type in order to form an n-channel thin filmtransistor. An impurity element 312 imparting n-type conductivity isadded to the semiconductor layer 302 provided with the mask layer 309,the first gate electrode layer 307, and the second gate electrode layer308; thereby a first n-type impurity region 314 a, a first n-typeimpurity region 314 b, a second n-type impurity region 313 a, and asecond n-type impurity region 313 b are formed (see FIG. 1C). Moreover,the semiconductor layer 302 of a region to which the impurity element312 is not added becomes a channel forming region 315.

The n-type impurity element 312 can be added to the semiconductor layer302 by using an ion doping method or an ion implanting method. Thesecond n-type impurity region 313 a and the second n-type impurityregion 313 b formed by adding the impurity element 312 imparting then-type conductivity to the semiconductor layer 302 of a region which isnot covered with the first gate electrode layer 307, the second gateelectrode layer 308, and the mask layer 309 correspond to highconcentration n-type impurity regions. On the other hand, the firstn-type impurity region 314 a and the first n-type impurity region 314 bformed by adding the impurity element 312 imparting n-type conductivityto the semiconductor layer 302 through the first gate electrode layer307 of a region which is not covered with the second gate electrodelayer 308 correspond to low concentration n-type impurity regions.

In this embodiment mode, the gate electrode layer has a stacked-layerstructure. By utilizing the different shapes of the first gate electrodelayer 307 and the second gate electrode layer 308, the first n-typeimpurity region 314 a, the first n-type impurity region 314 b, thesecond n-type impurity region 313 a, and the second n-type impurityregion 313 b are formed in a self-aligned manner by adding the impurityelement 312 imparting n-type conductivity once. In this embodiment mode,the second n-type impurity region 313 a, the second n-type impurityregion 313 b, the first n-type impurity region 314 a, and the firstn-type impurity region 314 b are formed by performing a step of addingthe impurity element once; however, the impurity regions can also beformed by a plurality of steps of adding the impurity element bycontrolling the thicknesses of the first gate electrode layer 307, thesecond gate electrode layer 308, and the gate insulating layer 303 andconditions of adding the impurity element.

The second n-type impurity region 313 a and the second n-type impurityregion 313 b which are high concentration n-type impurity regionsfunction as a source and a drain. On the other hand, the first n-typeimpurity region 314 a and the first n-type impurity region 314 b whichare low concentration n-type impurity regions correspond to LDD (LightlyDoped Drain) regions. In this specification, an impurity regionoverlapped with a gate electrode layer with a gate insulating layerinterposed therebetween is expressed as a Lov region while an impurityregion which is not overlapped with a gate electrode layer with a gateinsulating layer interposed therebetween is expressed as a Loff region.

In FIG. 1C, the impurity regions are expressed by hatching and white,which does not mean that an impurity element is not added to the whiteportion. They are expressed like this so that it is easily recognizedthat the concentration distribution of impurity elements in this regionreflects conditions of mask or doping. It is to be noted that this issimilar in other drawings of this specification.

The first gate electrode layer 307 is etched by using the second gateelectrode layer 308 as a mask; thereby a first gate electrode layer 316is formed (see FIG. 1D). The first gate electrode layer 316 reflects ashape of the second gate electrode layer 308 and has a shape in whichthe first gate electrode layer 307 of regions which extend outside thesecond gate electrode layer 308 are removed. Therefore, edge portions ofthe first gate electrode layer 316 and those of the second gateelectrode layer 308 almost correspond to each other. In this embodimentmode, when etching the first gate electrode layer 307, the mask layer309 is removed. The mask layer 309 may be removed after forming thefirst gate electrode layer 307 and the second gate electrode layer 308;however, it may be removed in the same step as forming the first gateelectrode layer 316 for simplifying the manufacturing steps.

As the first gate electrode layer 316 is formed, the first n-typeimpurity region 314 a and the first n-type impurity region 314 b areformed as Loff regions which are not covered with the first gateelectrode layer 316 and the second gate electrode layer 308 with thegate insulating layer 303 interposed therebetween. The first n-typeimpurity region 314 a or the first n-type impurity region 314 b formedas a Loff region on a drain side has an effect to alleviate an electricfield in the vicinity of the drain to prevent deterioration caused byhot carrier injection and to reduce an off current. As a result, asemiconductor device with high reliability and low power consumption canbe manufactured.

A wiring layer (also called a source electrode layer or a drainelectrode layer, not shown in FIGS. 1A to 1D) electrically connected tothe second n-type impurity region 313 a and the second n-type impurityregion 313 b which function as a source region and a drain region isformed, thereby an n-channel thin film transistor is manufactured.

Normally, when forming impurity regions with different concentrations inthe semiconductor layer in a non-self-aligned manner, desired length andarea of the impurity regions cannot be obtained in some cases because ofmisalignment in processing a mask layer used when forming the impurityregion. When the desired impurity region is not formed, desired devicecharacteristics of the thin film transistor cannot be obtained.Moreover, the device characteristics of a plurality of thin filmtransistors vary. Therefore, the reliability of the obtainedsemiconductor device is reduced.

Further, when the mask layer 309 is removed, the semiconductor layer 302cannot be protected from doping of impurity elements in some cases.

By the invention, a highly reliable semiconductor device can bemanufactured through simplified steps. Therefore, a semiconductor deviceand a display device with high resolution and high image quality can bemanufactured at low cost and high yield.

Embodiment Mode 2

A manufacturing method of a thin film transistor of this embodiment modeis described in details with reference to FIGS. 2A to 2F. In thisembodiment mode, two kinds of thin film transistors having gateelectrode layers with different structures are manufactured in the samestep as an example.

Similarly to Embodiment Mode 1, an insulating layer 321 as a base filmis formed over a substrate 320, and then semiconductor layers 322 a and322 b, and a gate insulating layer 323 covering the semiconductor layers322 a and 322 b are formed (see FIG. 2A). The semiconductor layers 322 aand 322 b may be doped with a slight amount of impurity element (boron(B) or phosphorus (P)) for controlling a threshold voltage of a thinfilm transistor.

A first conductive film 324 and a second conductive film 325 are formedover the gate insulating layer 323, and mask layers 326 a and 326 b areformed of resists for processing the aforementioned films into desiredshapes (see FIG. 2B). Similarly to the mask layer 306 described inEmbodiment Mode 1, the mask layers 326 a and 326 b are also formed byusing an exposure mask provided with a diffraction grating pattern or anauxiliary pattern formed of a semi-transmissive film having a lightintensity reducing function. With such an exposure mask, various lightexposures can be more accurately controlled, which enables a resist tobe processed into a more accurate shape. Therefore, when such a masklayer is used, the conductive film and the insulating film can beprocessed in the same step into different shapes in accordance withdesired performances. As a result, thin film transistors with differentcharacteristics, wires in different sizes and shapes, and the like canbe manufactured without increasing the number of steps.

The first conductive film 324 and the second conductive film 325 areetched by using the mask layers 326 a and 326 b; thereby a first gateelectrode layer 327 a, a first gate electrode layer 327 b, a second gateelectrode layer 328 a, and a second gate electrode layer 328 b areformed (see FIG. 2C). It is to be noted that when etching the firstconductive film 324 and the second conductive film 325, the mask layers326 a and 326 b are also etched to be mask layers 329 a and 329 brespectively. The shapes of the first gate electrode layer 327 a, thefirst gate electrode layer 327 b, the second gate electrode layer 328 a,and the second gate electrode layer 328 b reflect the shapes of the masklayers 326 a and 326 b. In this embodiment mode, the widths of the firstgate electrode layers 327 a and 327 b are wider than those of the secondgate electrode layers 328 a and 328 b. The first gate electrode layers327 a and 327 b extend to exist outside the side edge portions of thesecond gate electrode layers 328 a and 328 b respectively. For theetching, dry etching, wet etching, or the like can be used.

A mask layer 397 a covering the semiconductor layer 322 a, the firstgate electrode layer 327 a, and the second gate electrode layer 328 a isformed, and an impurity element imparting one conductivity type isintroduced to the semiconductor layer 322 b to form an impurity region.In the step shown in FIG. 2D, an impurity element imparting n-typeconductivity (in this embodiment mode, phosphorus (P)) is used as theimpurity element imparting one conductivity type in order to form ann-channel transistor.

An impurity element 330 imparting n-type conductivity is added to thesemiconductor layer 322 b provided with the first gate electrode layer327 b, the second gate electrode layer 328 b, and the mask layer 329 b,thereby a first n-type impurity region 334 a, a first n-type impurityregion 334 b, a second n-type impurity region 333 a, and a second n-typeimpurity region 333 b are formed (see FIG. 2D). Moreover, thesemiconductor layer 322 b of a region to which the impurity element 330is not added corresponds to a channel forming region 335. It is to benoted that the semiconductor layer 322 a is protected by the mask layer397 a from the impurity element 330.

The second n-type impurity region 333 a and the second n-type impurityregion 333 b formed by adding the impurity element 330 imparting n-typeconductivity to the semiconductor layer 322 b of a region which is notcovered with the first gate electrode layer 327 b, the second gateelectrode layer 328 b, and the mask layer 329 b correspond to highconcentration n-type impurity regions. On the other hand, the firstn-type impurity region 334 a and the first n-type impurity region 334 bformed by adding the impurity element 330 imparting n-type conductivityto the semiconductor layer 322 b through the first gate electrode layer327 b of a region which is not covered with the second gate electrodelayer 328 b correspond to low concentration n-type impurity regions. Inthis embodiment mode, the gate electrode layer has a stacked-layerstructure. By utilizing the different shapes of the first gate electrodelayer 327 b and the second gate electrode layer 328 b, the first n-typeimpurity region 334 a, the first n-type impurity region 334 b, thesecond n-type impurity region 333 a, and the second n-type impurityregion 333 b are formed in a self-aligned manner by adding the impurityelement 330 imparting n-type conductivity once.

Each impurity region may be formed by adding the impurity element 330imparting n-type conductivity a plurality of times or once. Bycontrolling doping conditions to add the impurity element, whether thefirst n-type impurity regions 334 a and 334 b and the second n-typeimpurity regions 333 a and 333 b are formed by an adding step of once ora plurality of times can be selected.

The second n-type impurity regions 333 a and 333 b are highconcentration n-type impurity regions which function as a source regionand a drain region. On the other hand, the first n-type impurity regions334 a and 334 b are low concentration n-type impurity regions whichfunction as LDD regions. In this embodiment mode, the first n-typeimpurity regions 334 a and 334 b are Lov regions covered with the firstgate electrode layer 327 b with the gate insulating layer 323 interposedtherebetween, which can alleviate an electric field in the vicinity ofthe drain region and suppress deterioration of an on current due to hotcarriers.

In this embodiment mode, after the mask layers 397 a and 329 b areremoved, a mask layer 397 b covering the first gate electrode layer 327b, the second gate electrode layer 328 b, and the semiconductor layer322 b is formed. As an impurity element imparting one conductivity type,an impurity element imparting p-type conductivity (in this embodimentmode, boron (B)) is added to the semiconductor layer 322 a to form animpurity region. In this embodiment mode, an impurity element 332imparting p-type conductivity is added to the semiconductor layer 322 aprovided with the first gate electrode layer 327 a and the second gateelectrode layer 328 a, thereby a first p-type impurity region 387 a, afirst p-type impurity region 387 b, a second p-type impurity region 386a, and a second p-type impurity region 386 b are formed (see FIG. 2E).Moreover, the semiconductor layer 322 a of a region to which theimpurity element 332 is not added functions as a channel forming region388. It is to be noted that the semiconductor layer 322 b is protectedby the mask layer 397 b from the impurity element 332.

The second p-type impurity region 386 a and the second p-type impurityregion 386 b formed by adding the impurity element 332 imparting p-typeconductivity to the semiconductor layer 322 a of a region which is notcovered with the first gate electrode layer 327 a and the second gateelectrode layer 328 a correspond to high concentration p-type impurityregions. On the other hand, the first p-type impurity region 387 a andthe first p-type impurity region 387 b formed by adding the impurityelement 332 imparting p-type conductivity to the semiconductor layer 322a though the first gate electrode layer 327 a of a region which is notcovered with the second gate electrode layer 328 a correspond to lowconcentration p-type impurity regions.

Each impurity region may be formed by adding the impurity element 332imparting p-type conductivity to the semiconductor layer 322 a aplurality of times or once. In this embodiment mode, the first p-typeimpurity region 387 a and the first p-type impurity region 387 b have animpurity element imparting p-type conductivity at a concentration lowerthan the second p-type impurity region 386 a and the second p-typeimpurity region 386 b; however, depending on the conditions to add theimpurity element, the impurity region under the first gate electrodelayer 327 a has a lower impurity concentration than the impurity regionwhich is not covered with the first gate electrode layer 327 a in somecases. Therefore, the first p-type impurity region 387 a and the firstp-type impurity region 387 b have impurity elements imparting p-typeconductivity at a concentration higher than or equal to the secondp-type impurity region 386 a and the second p-type impurity region 386b.

The first gate electrode layer 327 a is etched by using the second gateelectrode layer 328 a as a mask; thereby a first gate electrode layer336 is formed. The first gate electrode layer 336 has a shape in whichthe first gate electrode layer 327 a of regions which extend to existoutside the second gate electrode layer 328 a are removed, whichreflects a shape of the second gate electrode layer 328 a. Therefore,edge portions of the first gate electrode layer 336 and those of thesecond gate electrode layer 328 a almost correspond to each other.

The second p-type impurity region 386 a and the second p-type impurityregion 386 b are high concentration p-type impurity regions whichfunction as a source and a drain. On the other hand, the first p-typeimpurity region 387 a and the first p-type impurity region 387 b are lowconcentration p-type impurity regions which function as LDD regions. Asthe first gate electrode layer 336 is formed, the first p-type impurityregion 387 a and the first p-type impurity region 387 b are formed asLoff regions which are not covered with the first gate electrode layer336 and the second gate electrode layer 328 a with the gate insulatinglayer 323 interposed therebetween. The first p-type impurity region 387a or the first p-type impurity region 387 b formed as the Loff regionson the drain side have an effect to reduce an off current.

After the insulating layer 331 is formed and openings to reach eachsource region and drain region are formed therein, a source electrodelayer or a drain electrode layer 369 a and a source electrode layer or adrain electrode layer 369 b which are electrically connected to thesecond p-type impurity region 386 a and the second p-type impurityregion 386 b which function as a source region and a drain regionrespectively, and, a source electrode layer or a drain electrode layer369 c and a source electrode layer or a drain electrode layer 369 dwhich are electrically connected to the second n-type impurity region333 a and the second n-type impurity region 333 b which function as asource region and a drain region respectively are formed (see FIG. 2F).By the aforementioned steps, a p-channel thin film transistor 339 a andan n-channel thin film transistor 339 b are manufactured. Byelectrically connecting the p-channel thin film transistor 339 a and then-channel thin film transistor 339 b, a CMOS structure can bemanufactured.

By the invention, a highly reliable semiconductor device can bemanufactured through simplified steps. Therefore, a semiconductor deviceand a display device with high resolution and high image quality can bemanufactured at low cost and high yield.

Embodiment Mode 3

A manufacturing method of a thin film transistor of this embodiment modeis described in details with reference to FIGS. 3A to 3E. In thisembodiment mode, two kinds of thin film transistors having gateelectrode layers with different structures are manufactured in the samestep as an example.

Similarly to Embodiment Mode 1, an insulating layer 341 as a base filmis formed over a substrate 340, and then semiconductor layers 342 a and342 b, and a gate insulating layer 343 covering the semiconductor layers342 a and 342 b are formed. The semiconductor layers 342 a and 342 b maybe doped with a slight amount of impurity elements (boron (B) orphosphorus (P)) for controlling a threshold voltage of a thin filmtransistor.

A first conductive film 344 and a second conductive film 345 are formedover the gate insulating layer 343, and mask layers 346 a and 346 b areformed of resists for processing the aforementioned films into desiredshapes (see FIG. 3A). Similarly to the mask layer 306 described inEmbodiment Mode 1, the mask layers 346 a and 346 b are also formed byusing an exposure mask provided with a diffraction grating pattern or anauxiliary pattern formed of a semi-transmissive film having a lightintensity reducing function. With such an exposure mask, various lightexposures can be more accurately controlled, which enables a resist tobe processed into a more accurate shape. Therefore, when such a masklayer is used, the conductive film and the insulating film can beprocessed in the same step into different shapes in accordance withdesired performances. As a result, thin film transistors with differentcharacteristics, wires in different sizes and shapes, and the like canbe manufactured without increasing the number of steps.

The first conductive film 344 and the second conductive film 345 areetched by using the mask layers 346 a and 346 b; thereby a first gateelectrode layer 347 a, a first gate electrode layer 347 b, a second gateelectrode layer 348 a, and a second gate electrode layer 348 b areformed (see FIG. 3B). It is to be noted that when etching the firstconductive film 344 and the second conductive film 345, the mask layers346 a and 346 b are also etched to be mask layers 349 a and 349 brespectively. The shapes of the first gate electrode layer 347 a, thefirst gate electrode layer 347 b, the second gate electrode layer 348 a,and the second gate electrode layer 348 b reflect the shapes of the masklayers 346 a and 346 b. In this embodiment mode, the widths of the firstgate electrode layers 347 a and 347 b are wider than those of the secondgate electrode layers 348 a and 348 b. The first gate electrode layers347 a and 347 b extend to exist outside the side edge portions of thesecond gate electrode layers 348 a and 348 b respectively. For etchingthe first conductive film 344 and the second conductive film 345, dryetching, wet etching, or the like can be used.

By introducing impurity elements imparting one conductivity type to thesemiconductor layers 342 a and 342 b, impurity regions are formed. Inthis embodiment mode, an impurity element 352 imparting n-typeconductivity (in this embodiment mode, phosphorus (P)) is used as theimpurity element imparting one conductivity type to form an n-channelthin film transistor. The impurity element 352 imparting n-typeconductivity is added to the semiconductor layers 342 a and 342 bprovided with the first gate electrode layer 347 a, the first gateelectrode layer 347 b, the second gate electrode layer 348 a, and thesecond gate electrode layer 348 b, thereby a first n-type impurityregion 354 a, a first n-type impurity region 354 b, a first n-typeimpurity region 354 c, a first n-type impurity region 354 d, a secondn-type impurity region 353 a, a second n-type impurity region 353 b, asecond n-type impurity region 353 c, and a second n-type impurity region353 d are formed (see FIG. 3C). The semiconductor layers 342 a and 342 bof regions to which the impurity element 352 is not added function as achannel forming region 355 a and a channel forming region 355 b.

The second n-type impurity region 353 a, the second n-type impurityregion 353 b, the second n-type impurity region 353 c, and the secondn-type impurity region 353 d formed by adding the impurity element 352imparting n-type conductivity to the semiconductor layer 342 a and thesemiconductor layer 342 b of regions which are not covered with thefirst gate electrode layer 347 a, the first gate electrode layer 347 b,the second gate electrode layer 348 a, the second gate electrode layer348 b, the mask layer 349 a, and the mask layer 349 b correspond to highconcentration n-type impurity regions. On the other hand, the firstn-type impurity region 354 a, first n-type impurity region 354 b, firstn-type impurity region 354 c, and first n-type impurity region 354 dformed by adding the impurity element 352 imparting n-type conductivityto the semiconductor layer 342 a and the semiconductor layer 342 bthrough the first gate electrode layer 347 a and the first gateelectrode layer 347 b of regions which are not covered with the secondgate electrode layer 348 a and the second gate electrode layer 348 bcorrespond to low concentration n-type impurity regions. In thisembodiment mode, the gate electrode layer has a stacked-layer structure.By utilizing the different shapes of the first gate electrode layer 347a, the first gate electrode layer 347 b, the second gate electrode layer348 a, and the second gate electrode layer 348 b, the first n-typeimpurity region 354 a, the first n-type impurity region 354 b, the firstn-type impurity region 354 c, the first n-type impurity region 354 d,the second n-type impurity region 353 a, the second n-type impurityregion 353 b, the second n-type impurity region 353 c, and the secondn-type impurity region 353 d are formed in a self-aligned manner byadding the impurity element 352 imparting n-type conductivity once.

Each impurity region may be formed by adding the impurity element 352imparting n-type conductivity a plurality of times or once. Bycontrolling doping conditions to add the impurity element, either thefirst n-type impurity regions 354 a, 354 b, 354 c, and 354 d and thesecond n-type impurity regions 353 a, 353 b, 353 c, and 353 d are formedby an adding step of once or a plurality of times can be selected.

A mask layer 357 covering the first gate electrode layer 347 b, thesecond gate electrode layer 348 b, and the semiconductor layer 342 b isformed and the first gate electrode layer 347 a is etched by using thesecond gate electrode layer 348 a as a mask; thereby a first gateelectrode layer 356 is formed (see FIG. 3D). The first gate electrodelayer 356 has a shape in which regions of the first gate electrode layer347 a which extend to exist outside the second gate electrode layer 348a are removed, which reflects a shape of the second gate electrode layer348 a. Therefore, edge portions of the first gate electrode layer 356and those of the second gate electrode layer 348 a almost correspond toeach other.

Further, in this embodiment mode, the mask layer 349 a and the masklayer 349 b are used as protective layers for the second gate electrodelayer 348 a and the second gate electrode layer 348 b in the step ofadding the impurity element 352, and removed after the step of addingthe impurity element 352.

The second n-type impurity region 353 a, the second n-type impurityregion 353 b, the second n-type impurity region 353 c, and the secondn-type impurity region 353 d which are high concentration n-typeimpurity regions function as source regions and drain regions. On theother hand, the first n-type impurity region 354 a, the first n-typeimpurity region 354 b, the first n-type impurity region 354 c, and thefirst n-type impurity region 354 d which are low concentration n-typeimpurity regions function as LDD regions.

As the first gate electrode layer 356 is formed, the first n-typeimpurity region 354 a and the first n-type impurity region 354 b areformed as Loff regions which are not covered with the first gateelectrode layer 356 and the second gate electrode layer 348 a with thegate insulating layer 343 interposed therebetween. The first n-typeimpurity region 354 a or the first n-type impurity region 354 b formedas a Loff region on a drain side has effects to alleviate an electricfield in the vicinity of the drain region to prevent deteriorationcaused by hot carrier injection and to reduce an off current. As aresult, a semiconductor device with high reliability and low powerconsumption can be manufactured.

On the other hand, the first n-type impurity region 354 c and the firstn-type impurity region 354 d which are covered with the first gateelectrode layer 347 b with the gate insulating layer 343 interposedtherebetween are Lov regions which can alleviate an electric field inthe vicinity of the drain region to prevent deterioration of an oncurrent caused by hot carrier injection.

After forming an insulating layer 398 and openings to reach respectivesource regions and drain regions in the insulating layer 398, a sourceelectrode layer or a drain electrode layer 358 a and a source electrodelayer or a drain electrode layer 358 b which are electrically connectedto the second n-type impurity region 353 a and the second n-typeimpurity region 353 b respectively which function as a source region anda drain region, a source electrode layer or a drain electrode layer 358c and a source electrode layer or a drain electrode layer 358 d whichare electrically connected to the second n-type impurity region 353 cand the second n-type impurity region 353 d respectively which functionas a source region and a drain region are formed. By the aforementionedsteps, an n-channel thin film transistor 359 a and an n-channel thinfilm transistor 359 b are formed (see FIG. 3E). By electricallyconnecting the n-channel thin film transistor 359 a and the n-channelthin film transistor 359 b, a circuit with an NMOS structure can bemanufactured.

Further, when an impurity element imparting n-type conductivity (forexample, phosphorus (P)) is used as an impurity element imparting oneconductivity type to be added as in this embodiment mode, an n-channelthin film transistor having an impurity region with n-type conductivitycan be formed. When an impurity element imparting p-type conductivity(for example, boron (B)) is used as an impurity element imparting oneconductivity type to be added, a p-channel thin film transistor havingan impurity region with p-type conductivity can be similarly formed.

By the invention, a highly reliable semiconductor device can bemanufactured through simplified steps. Therefore, a semiconductor deviceand a display device with high resolution and high image quality can bemanufactured at low cost and high yield.

Embodiment Mode 4

A manufacturing method of a thin film transistor of this embodiment modeis described in details with reference to FIGS. 4A to 4F. In thisembodiment mode, two kinds of thin film transistors having gateelectrode layers with different structures and a capacitor aremanufactured in the same step as an example.

Similarly to Embodiment Mode 1, an insulating layer 361 as a base filmis formed over a substrate 360, and then semiconductor layers 362 a, 362b, and 362 c, and a gate insulating layer 363 covering the semiconductorlayers 362 a, 362 b, and 362 c are formed (see FIG. 4A). Thesemiconductor layers 362 a and 362 b may be doped with a slight amountof impurity element (boron (B) or phosphorus (P)) for controlling athreshold voltage of a thin film transistor.

A first conductive film 364 and a second conductive film 365 are formedover the gate insulating layer 363, and mask layers 366 a, 366 b, and366 c are formed of resists for processing the aforementioned films intodesired shapes (see FIG. 4A). Similarly to the mask layer 306 describedin Embodiment Mode 1, the mask layers 366 a, 366 b, and 366 c are alsoformed by using an exposure mask provided with a diffraction gratingpattern or an auxiliary pattern formed of a semi-transmissive filmhaving a light intensity reducing function.

An exposure mask provided with a diffraction grating pattern or anauxiliary pattern formed of a semi-transmissive film having a lightintensity reducing function which is used in this embodiment mode isdescribed with reference to FIGS. 19A and 19B. By the light intensityreducing function of the semi-transmissive film, the intensity of lightpassing therethrough can be reduced to 10 to 70%.

FIG. 19A is a sectional view showing an exposure step for forming themask layers 366 a, 366 b, and 366 c. FIGS. 19A and 19B correspond toFIG. 4A, in which the semiconductor layers 362 a, 362 b, and 362 c areprovided over the substrate 360 and the insulating layer 361, while thegate insulating layer 363, the first conductive film 364, the secondconductive film 365, and a resist film 760 are formed so as to cover thesemiconductor layers 362 a, 362 b, and 362 c. In this embodiment mode, apositive type resist in which a region exposed to light is removed isused.

An exposure mask is provided over the resist film 760 with an opticalsystem interposed therebetween. The exposure mask has light shieldingportions 752 a, 752 b, and 752 c formed of metal films such as Cr and aportion provided with semi-transmissive films 751 a, 751 b, and 751 c asan auxiliary pattern.

In FIG. 19A, an exposure mask has the semi-transmissive films 751 a, 751b, and 751 c formed of MoSiN over a light transmissive substrate 750 andthe light shielding portions 752 a, 752 b, and 752 c formed of metalfilms such as Cr so as to be stacked over the semi-transmissive films751 a, 751 b, and 751 c respectively. The semi-transmissive films 751 a,751 b, and 751 c can be formed by using MoSi, MoSiO, MoSiON, CrSi, orthe like as well as MoSiN.

By performing light exposure to the resist films by using the exposuremask shown in FIG. 19A, a light-exposed region 762, light-unexposedregions 761 a, 761 b, and 761 c are formed. In the case of lightexposure, light passes around the light shielding portions and throughthe semi-transmissive films; thereby an exposed region 762 shown in FIG.19A is formed.

When developed, the exposed region 762 is removed and mask layers 366 a,366 b, and 366 c as resist patterns shown in FIG. 19B (corresponding toFIG. 4A) are obtained.

As an example of another exposure mask, an exposure mask provided with adiffraction grating pattern with a plurality of slits between theshielding portions may be used. A diffraction grating pattern is apattern provided with at least one opening pattern such as a slit, adot, or the like. When a plurality of openings are provided, theopenings may be arranged regularly (periodically) in some order orrandomly (non-periodically). By using a diffraction grating patternhaving an opening (space) with a fine width of the resolution of anexposure apparatus or narrower and a non-opening (line), a substantialamount of light exposure can be changed and a thickness of an exposedresist film after development can be controlled. The resolution is thenarrowest possible width formed by the exposure apparatus. In aprojection exposure apparatus, a resolution R is expressed as R=Kλ/NA. Kis a constant, λ is a wavelength of light used for exposure, and NA isthe number of openings of the projection lens. Therefore, when theresist film is processed by the method shown in FIGS. 19A and 19B, theresist film can be selectively processed finely without increasing thenumber of steps; thereby various resist patterns (mask layers) can beobtained. By using such a resist pattern (mask layer), two kinds of thinfilm transistors having gate electrode layers with different shapes anda capacitor are formed in this embodiment mode.

In FIG. 4A, the first conductive film 364 and the second conductive film365 are formed, and the mask layers 366 a, 366 b, and 366 c in differentshapes formed as shown in FIGS. 19A and 19B are formed.

The mask layer 366 a has a shape like a rectangular solid without anysteps, projections or depressions. The mask layer 366 b has a shape withgentle steps at edge portions. The mask layer 366 c has a shape with aprojection near an edge portion.

Etching treatment is carried out by using the mask layers 366 a, 366 b,and 366 c to form a first gate electrode layer 367 a, a second gateelectrode layer 368 a, a first gate electrode layer 367 b, a second gateelectrode layer 368 b, a first conductive layer 765, and a secondconductive layer 766 are formed (see FIG. 4B). Edge portions of thefirst gate electrode layer 367 a and those of the second gate electrodelayer 368 a almost correspond to each other and are continuous. On theother hand, the first gate electrode layer 367 b has a wider width thanthe second gate electrode layer 368 b. The first gate electrode layer367 b extends to exist outside edge portions of the second gateelectrode layer 368 b. As for the first conductive layer 765 and thesecond conductive layer 766 which reflect the shape of the mask layer366 c, similarly to the first gate electrode layer 367 a and the secondgate electrode layer 367 b, the first conductive layer 765 has a widerwidth than the second conductive layer 766 and extends to exist outsideone edge portion of the second conductive layer 766. A top edge portionof one side of the first conductive layer 765 almost corresponds to abottom edge portion of one side of the second conductive layer 766. Asshown in FIG. 4B, the second conductive layer 766 has a narrower widththan the first gate electrode layer 368 b and covers a smaller region ofthe first conductive layer 765. Therefore, a larger region of the firstconductive layer 765 is exposed.

A mask layer 396 a covering the semiconductor layer 362 a, the firstgate electrode layer 367 a, and the second gate electrode layer 368 a isformed, an impurity element imparting one conductivity type isintroduced to the semiconductor layer 362 b provided with the first gateelectrode layer 367 b and the second gate electrode layer 368 b and thesemiconductor layer 362 c provided with the first conductive layer 765and the second conductive layer 766, thereby impurity regions areformed. In the step shown in FIG. 4C, an impurity element impartingn-type conductivity (in this embodiment mode, phosphorus (P)) is used asan impurity element imparting one conductivity type.

By adding an impurity element 380 imparting n-type conductivity to thesemiconductor layer 362 b provided with the first gate electrode 367 band the second gate electrode layer 368 b and the semiconductor layer362 c over which the first conductive layer 765 and the secondconductive layer 766 are provided, a first n-type impurity region 374 a,a first n-type impurity region 374 b, a second n-type impurity region373 a, a second n-type impurity region 373 b, a first n-type impurityregion 394, and a second n-type impurity region 393 are formed (see FIG.4C). Moreover, the semiconductor layer 362 b of a region to which theimpurity element 380 is not added functions as a channel forming region377. Similarly, the semiconductor layer 362 c of a region to which theimpurity element 380 is not added functions as a non-impurity addedregion 319. It is to be noted that the semiconductor layer 362 a isprotected by the mask layer 396 a from the impurity element 380.

The second n-type impurity region 373 a, the second n-type impurityregion 373 b, and the second n-type impurity region 393 which are formedby adding the impurity element 380 imparting n-type conductivity to thesemiconductor layers 362 b and 362 c of regions which are not coveredwith the first gate electrode layer 367 b, the second gate electrodelayer 368 b, the first conductive layer 765 and the second conductivelayer 766 correspond to high concentration n-type impurity regions. Onthe other hand, the first n-type impurity region 374 a, the first n-typeimpurity region 374 b, and the first n-type impurity region 394 formedby adding the impurity element 380 imparting n-type conductivity throughthe first gate electrode layer 367 b and the first conductive layer 765of regions which are not covered with the second gate electrode layer368 b and the second conductive layer 766 correspond to lowconcentration n-type impurity regions. In this embodiment mode, a gateelectrode layer has a stacked-layer structure. The first n-type impurityregion 374 a, the first n-type impurity region 374 b, the first n-typeimpurity region 394, the second n-type impurity region 373 a, the secondn-type impurity region 373 b, and the second n-type impurity region 393are formed in a self-aligned manner by adding the impurity element 380imparting n-type conductivity once by utilizing the different shapes ofthe first gate electrode layer 367 b, the second gate electrode layer368 b, the first conductive layer 765, and the second conductive layer766.

Each impurity region may be formed by adding the impurity element 380imparting n-type conductivity a plurality of times or once. Bycontrolling doping conditions to add the impurity element, whether thefirst n-type impurity region 374 a, the first n-type impurity region 374b, the first n-type impurity region 394, the second n-type impurityregion 373 a, the second n-type impurity region 373 b, and the secondn-type impurity region 393 are formed by an adding step of once or aplurality of times can be selected.

The second n-type impurity regions 373 a and 373 b which are highconcentration n-type impurity regions function as a source region and adrain region. On the other hand, the first n-type impurity regions 374 aand 374 b which are low concentration n-type impurity regions functionas LDD regions.

A mask layer 396 b covering the semiconductor layer 362 b and thesemiconductor layer 362 c is formed and an impurity element 382imparting p-type conductivity (in this embodiment mode, boron (B)) isadded to the semiconductor layer 362 a as an impurity element impartingone conductivity type; thereby a p-type impurity region 381 a and ap-type impurity region 381 b are formed (see FIG. 4D). In thisembodiment mode, the p-type impurity region 381 a and the p-typeimpurity region 381 b are formed in a self-aligned manner by using thefirst gate electrode layer 367 a and the second gate electrode layer 368a as masks; therefore, a low concentration impurity region is notintentionally formed in the semiconductor layer 362 a, and all theimpurity regions can be high concentration impurity regions.

A mask layer 396 d covering the semiconductor layer 362 a, the firstconductive layer 367 a, and the second gate electrode layer 368 a, and amask layer 396 c covering the semiconductor layer 362 c, the firstconductive layer 765, and the second conductive layer 766 are formed andthe first gate electrode layer 367 b is etched by using the second gateelectrode layer 368 b as a mask; thereby a first gate electrode layer376 is formed (see FIG. 4E). The first gate electrode layer 376 has ashape in which the first gate electrode layer 367 b of regions whichextend to exist outside the second gate electrode layer 368 b areremoved, which reflects a shape of the second gate electrode layer 368b. Therefore, edge portions of the first gate electrode layer 376 andthose of the second gate electrode layer 368 b almost correspond to eachother.

As the first gate electrode layer 376 is formed, the first n-typeimpurity region 374 a and the first n-type impurity region 374 b areformed as Loff regions which are not covered with the first gateelectrode layer 376 and the second gate electrode layer 368 b with thegate insulating layer 363 interposed therebetween. The first n-typeimpurity region 374 a or the first n-type impurity region 374 b formedas a Loff region on a drain side has effects to alleviate an electricfield in the vicinity of the drain region to prevent deteriorationcaused by hot carrier injection and to reduce an off current. As aresult, a semiconductor device with high reliability and low powerconsumption can be manufactured.

After forming an insulating layer 399 and forming openings to reachrespective source regions and drain regions in the insulating layer 399and an opening to reach the second n-type impurity region 393, a sourceelectrode layer or a drain electrode layer 383 a and a source electrodelayer or a drain electrode layer 383 b which are electrically connectedrespectively to the p-type impurity region 381 a and the p-type impurityregion 381 b which function as a source region and a drain region, asource electrode layer or a drain electrode layer 383 c, a sourceelectrode layer or a drain electrode layer 383 d, and a wiring layer 767which are electrically connected respectively to the second n-typeimpurity region 373 a and the second n-type impurity region 373 b whichfunction as a source region and a drain region, and the second n-typeimpurity region 393 are formed. By the aforementioned steps, a p-channelthin film transistor 385 having no LDD region (what is called a singledrain type transistor), an n-channel thin film transistor 375 having anLDD region in a Loff region, and a capacitor 395 are formed (see FIG.4F).

When an impurity element imparting n-type conductivity (for example,phosphorus (P)) is used as an impurity element imparting oneconductivity type to be added, an n-channel thin film transistor havingan impurity region with n-type conductivity can be formed. When animpurity element imparting p-type conductivity (for example, boron (B))is used as an impurity element imparting one conductivity type to beadded, a p-channel thin film transistor having an impurity region withp-type conductivity can be formed.

By controlling doping conditions or the like to add an impurity elementimparting one conductivity type, all the impurity regions can be formedas high concentration impurity regions without forming a lowconcentration impurity region.

In the same step, thin film transistors having gate electrode layers andimpurity regions with different structures can be formed. Moreover, inthe case of forming a wire or the like in the same step, a wire withlower resistance or a wire in a smaller size can be formed. As a result,further fineness can be achieved, which realizes higher precision,higher performance, lighter weight, and the like of a semiconductordevice.

The capacitor 395 can have a shape in which the first conductive layer765 is wider than the second conductive layer 766; therefore, a regionof the first n-type impurity region 394 can be formed wide. Capacitanceformed between the impurity region and the gate electrode is larger thanthat formed between the non-impurity added region 319 and the gateelectrode. Thus, by forming the first n-type impurity region 394 underthe first conductive layer 765 wider, large capacitance can be obtained.

In this manner, by using this embodiment mode, a conductive film and aninsulating film can be processed into different shapes in accordancewith a desired performance in the same step. Therefore, thin filmtransistors with different characteristics, wires in different sizes orshapes, or the like can be manufactured without increasing the number ofsteps. This embodiment mode can be freely implemented in combinationwith each of Embodiment Modes 1 to 3.

By the invention, a highly reliable semiconductor device can bemanufactured through simplified steps. Therefore, a semiconductor deviceand a display device with high resolution and high image quality can bemanufactured at low cost and high yield.

Embodiment Mode 5

A manufacturing method of a display device of this embodiment mode isdescribed in details with reference to FIGS. 5A to 10B and 20A to 21B.

FIG. 20A is a top plan view showing a configuration of a display panelof the invention. A pixel portion 2701 in which pixels 2702 are arrangedin matrix, a scan line input terminal 2703, and a signal line inputterminal 2704 are formed over a substrate 2700 having an insulatingsurface. The number of pixels may be any number in accordance withvarious standards. An XGA display requires 1024×768×3 (RGB), an UXGAdisplay requires 1600×1200×3 (RGB), and a full-spec high vision displayrequires 1920×1080×3 (RGB) pixels.

The pixels 2702 are arranged in matrix in accordance with scan linesextending from the scan line input terminal 2703 and signal linesextending from the signal line input terminal 2704 intersecting eachother. Each pixel 2702 has a switching element and a pixel electrodelayer connected thereto. A typical example of a switching element is aTFT. Each pixel can be independently controlled by an externallyinputted signal due to a structure of a TFT where a gate electrode layerside is connected to the scan line while a source or drain side isconnected to the signal line.

FIG. 20A shows a configuration of a display panel in which signalsinputted to the scan line and the signal line are controlled by externaldriver circuits. Meanwhile, as shown in FIG. 21A, a driver IC 2751 maybe mounted on the substrate 2700 by a COG (Chip On Glass) method. Asanother mode, a TAB (Tape Automated Bonding) method as shown in FIG. 21Bmay also be used. The driver IC may be formed over a single crystallinesemiconductor substrate or formed of TFTs over a glass substrate. Ineach of FIGS. 21A and 21B, the driver IC 2751 is connected to an FPC(Flexible Printed Circuit) 2750.

When a TFT provided in a pixel is formed of a crystalline semiconductor,a scan line driver circuit 3702 may be formed over a substrate 3700 asshown in FIG. 20B. In FIG. 20B, a pixel portion 3701 is controlled by anexternal driver circuit which is connected to a signal line inputterminal 3704 similarly to FIG. 20A. When a TFT provided in a pixel isformed of a polycrystalline (microcrystalline) semiconductor, a singlecrystalline semiconductor, or the like having high mobility, a scan linedriver circuit 4702 and a signal line driver circuit 4704 can be formedto be integrated over a substrate 4700 in FIG. 20C.

Over a substrate 100 having an insulating surface, a base film 101 a isformed with a thickness of 10 to 200 nm (preferably, 50 to 150 nm) usinga silicon nitride oxide (SiNO) film by a sputtering method, a physicalvapor deposition (PVD) method, a chemical vapor deposition (CVD) methodsuch as a low-pressure CVD (LPCVD) method or a plasma CVD method, or thelike, and a base film 101 b is stacked thereover with a film thicknessof 50 to 200 nm (preferably, 100 to 150 nm) using a silicon oxynitride(SiON) film as a base film. Alternatively, acrylic acid, methacrylicacid, or a derivative thereof, a heat-resistant high molecular compoundsuch as polyimide, aromatic polyamide, or polybenzimidazole, or asiloxane resin may be used. Note that the siloxane resin corresponds toa resin containing a Si—O—Si bond. The skeletal structure of siloxane isconstituted by a bond of silicon (Si) and oxygen (O). As a substituent,an organic group containing at least hydrogen (for example, an alkylgroup or an aromatic hydrocarbon) is used. As the substituent, a fluorogroup may also be used. Alternatively, an organic group containing atleast hydrogen, and a fluoro group may be used as the substituent.Further, a vinyl resin such as polyvinyl alcohol, or polyvinyl butyral;or a resin material such as epoxy resin, phenol resin, novolac resin,acrylic resin, melamine resin, or urethane resin is used. Further, anorganic material such as benzocyclobutene, parylene,fluorinated-arylene-ether, or polyimide, or a composition materialcontaining a water-soluble homopolymer and a water-soluble copolymer maybe used. Further, an oxazole resin can also be used, for example, aphotosensitive polybenzoxazole or the like can be used. A photosensitivepolybenzoxazole has a low dielectric constant (a dielectric constant of2.9 at 1 MHz and a normal temperature), high heat resistance (TGA:Thermal Gravity Analysis) thermal decomposition temperature of 550° C.with the rise in temperature at 5° C./min), and a low moisture absorbingrate (0.3% in 24 hours at a normal temperature). It is to be noted thatthe moisture absorbing rate is expressed in a percentage of a ratio ofthe weight increase to the original weight after soaking a sample of acertain size in distilled water for some period of time.

A droplet discharge method, a printing method (a method for forming apattern, such as screen printing or offset printing), a coating methodsuch as a spin coating method, a dipping method, or the like may also beused. In this embodiment mode, the base films 101 a and 101 b are formedby a plasma CVD method. The substrate 100 may be a glass substrate, aquartz substrate, a silicon substrate, a metal substrate, or a stainlesssteel substrate having a surface covered with an insulating film.Further, a plastic substrate having heat resistance which can resist aprocessing temperature of this embodiment mode or a flexible substratesuch as a film may also be used. As a plastic substrate, a substrateformed of PET (polyethylene terephthalate), PEN (polyethylenenaphthalate), or PES (polyether sulfone) may be used, and as a flexiblesubstrate, a synthetic resin such as acrylic can be used. Since thedisplay device manufactured in the present embodiment mode has astructure in which light from the light-emitting element is emittedthrough the substrate 100, the substrate 100 is required to have a lighttransmissive property.

The base film can be formed of a single layer or a stacked-layerstructure of as two or three layers of silicon oxide, silicon nitride,silicon oxynitride, silicon nitride oxide, or the like. Note that inthis specification, silicon oxynitride means a substance where thecomposition ratio of oxygen is higher than that of nitrogen, which canalso be referred to as silicon oxide containing nitrogen. Meanwhile,silicon nitride oxide means a substance where the composition ratio ofnitrogen is higher than that of oxygen, which can also be referred to assilicon nitride containing oxygen. In this embodiment, a silicon nitrideoxide film with a thickness of 50 nm is formed over the substrate withSiH₄, NH₃, N₂O, N₂, and H₂ used as a reaction gas, and a siliconoxynitride film with a thickness of 100 nm is formed with SiH₄ and N₂Oused as a reaction gas. Alternatively, a silicon nitride oxide film witha thickness of 140 nm and a silicon oxynitride film with a thickness of100 nm may be stacked.

Subsequently, a semiconductor film is formed over the base films. Thesemiconductor film may be formed by a known method (a sputtering method,an LPCVD method, a plasma CVD method, or the like) to have a thicknessof 25 to 200 nm (preferably, 30 to 150 nm). In this embodiment mode, thesemiconductor film is preferably formed of a crystalline semiconductorfilm that is obtained by laser crystallization of an amorphoussemiconductor film.

The semiconductor film may be formed of an amorphous semiconductor(hereinafter also referred to as AS) that is formed by a vapordeposition method or a sputtering method using a semiconductor materialgas typified by silane and germane; a polycrystalline semiconductor thatis obtained by crystallizing the amorphous semiconductor utilizingoptical energy or heat energy; a semi-amorphous semiconductor (alsocalled microcrystal, hereinafter also referred to as SAS), or the like.

SAS is a semiconductor having an intermediate structure betweenamorphous and crystalline (including single crystalline andpolycrystalline) structures. This semiconductor has a third state thatis stable in free energy, and it includes a crystalline region that hasa short range order and a lattice distortion. SAS is obtained by glowdischarge decomposition (plasma CVD) of gas containing silicon. As thegas containing silicon, not only SiH4 but also Si₂H₆, SiH₂Cl₂, SiHCl₃,SiCl₄, SiF₄, or the like may be used. In addition, F₂ or GeF₄ may bemixed into the gas. The gas containing silicon may be diluted with H₂ orH₂ and one or more kinds of rare gas elements selected from He, Ar, Kr,and Ne. When a rare gas element such as helium, argon, krypton, and neonis mixed into SAS, the lattice distortion is further increased and thestability is thus enhanced, leading to a high quality SAS.Alternatively, as the semiconductor film, an SAS layer formed of afluorine-based gas and an SAS layer made of a hydrogen-based gas may bestacked.

An amorphous semiconductor is typified by hydrogenated amorphoussilicon, and a crystalline semiconductor is typified by polysilicon.Polysilicon (polycrystalline silicon) includes a so-called hightemperature polysilicon that mainly uses polysilicon formed at a processtemperature of 800° C. or higher, a so-called low temperaturepolysilicon that mainly uses polysilicon formed at a process temperatureof 600° C. or lower, a polysilicon that is obtained by crystallizationafter adding an element for promoting crystallization, and the like.Needless to say, a semi-amorphous semiconductor or a semiconductorpartially including a crystalline phase may also be used as set forthabove.

When a crystalline semiconductor film is formed as the semiconductorfilm, the crystalline semiconductor film may be formed by a known method(laser crystallization, thermal crystallization, thermal crystallizationusing an element for promoting crystallization such as nickel, or thelike). Alternatively, a microcrystalline semiconductor that is an SASmay be irradiated with a laser to be crystallized, thereby increasingthe crystallinity. If an element for promoting crystallization is notintroduced, an amorphous semiconductor film is heated at 500° C. for onehour in a nitrogen atmosphere before being irradiated with a laser beam,so that hydrogen included in the amorphous semiconductor film may bereleased to lower the hydrogen concentration to 1×10²⁰ atoms/cm³ orlower. This is performed because the amorphous semiconductor film isdamaged when the film containing much hydrogen is irradiated with laser.The heat treatment for crystallization may be performed using a heatingfurnace, laser irradiation, irradiation with light emitted from a lamp(hereinafter also referred to as lamp annealing), or the like. The heattreatment may also be performed by RTA such as GRTA (Gas Rapid ThermalAnnealing) and LRTA (Lamp Rapid Thermal Annealing). The GRTA is heattreatment using a high temperature gas, and the LRTA is heat treatmentusing lamp light.

In the step of forming a crystalline semiconductor layer bycrystallizing an amorphous semiconductor layer, an element (also calleda catalyst element or a metal element) which promotes crystallizationmay be added to the amorphous semiconductor layer and crystallizationmay be performed by heat treatment (3 minutes to 24 hours at 550 to 750°C.). One or a plurality selected from iron (Fe), nickel (Ni), cobalt(Co), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium(Ir), platinum (Pt), copper (Cu), and gold (Au) can be used as a metalelement which promotes crystallization of silicon.

A metal element may be introduced to the amorphous semiconductor film byany method as long as the metal element can exist on the surface orinside of the amorphous semiconductor film, and for example, sputtering,CVD, plasma treatment (including plasma CVD), adsorption, or a methodfor applying a metal salt solution can be used. Among them, the methodusing a solution is simple, and is effective in easily adjusting theconcentration of the metal element. Further, at this time, an oxide filmis desirably formed by UV ray irradiation in an oxygen atmosphere,thermal oxidation, treatment with ozone water or hydrogen peroxideincluding hydroxyl radical, or the like in order to improve thewettability of the surface of the amorphous semiconductor film and tospread the water solution over the entire surface of the amorphoussemiconductor film.

In order to remove or reduce the element which promotes crystallizationfrom the crystalline semiconductor layer, a semiconductor layercontaining an impurity element is formed in contact with the crystallinesemiconductor layer and used as a gettering sink. The impurity elementmay be an impurity element imparting n-type conductivity, an impurityelement imparting p-type conductivity, a rare gas element, or the like.For example, one or a plurality of elements selected from phosphorus(P), nitrogen (N), arsenic (As), antimony (Sb), bismuth (Bi), boron (B),helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe) can beused. A semiconductor layer containing a rare gas element is formed in acrystalline semiconductor layer containing an element which promotescrystallization, and thermal treatment is performed (3 minutes to 24hours at 550 to 750° C.). The element which promotes crystallizationcontained in the crystalline semiconductor layer moves into thesemiconductor layer containing a rare gas element. The element whichpromotes crystallization contained in the crystalline semiconductorlayer is removed or reduced. After that, the semiconductor layercontaining a rare gas element which is a gettering sink is removed.

By scanning such laser and the semiconductor film relatively, laserirradiation can be performed. Further, in the laser irradiation, amarker may be formed to overlap beams with high precision and controlpositions for starting and finishing laser irradiation. The marker maybe formed over the substrate at the same time when an amorphoussemiconductor film is formed.

In the case of laser irradiation, a continuous wave laser beam (CW laserbeam) or a pulsed wave laser beam (pulsed laser beam) can be used. Asthe laser beam, a laser beam oscillated from one or a plurality selectedfrom a gas laser such as Ar laser, Kr laser, and excimer laser, a singlecrystal of YAG laser, YVO₄ laser, forstelite (Mg₂SiO₄), YLF laser, YAlO₃laser, GdVO₄ laser, or a polycrystal (ceramic) of YAG, Y₂O₃, YVO₄,YAlO₃, or GdVO₄ doped with one or more kinds of Nd, Yb, Cr, Ti, Ho, Er,Tm, and Ta as a dopant, glass laser, ruby laser, alexandrite laser, Ti:sapphire laser, copper vapor laser, and gold vapor laser can be used. Byemitting a laser beam of second to fourth wave of a fundamental wave inaddition to a fundamental harmonic of the foregoing laser beams, acrystal having a large grain diameter can be obtained. For instance, asecond harmonic (532 nm) or a third harmonic (355 nm) of Nd:YVO₄ laser(fundamental, 1064 nm) can be used. This laser can be emitted by CW orpulsed oscillation. In the case of CW, the laser requires power densityof approximately from 0.01 to 100 MW/cm² (preferably, approximately from0.1 to 10 MW/cm²). The laser is emitted at a scanning rate ofapproximately 10 to 2000 cm/sec.

Note that, a laser using, as a medium, single crystal of YAG, YVO₄,forsterite (Mg₂SiO₄), YAlO₃, or GdVO₄ or polycrystal (ceramic) of YAG;Y₂O₃, YVO₄, YAlO₃, or GdVO₄ doped with one or more of Nd, Yb, Cr, Ti,Ho, Er, Tm, and Ta as a dopant; an Ar ion laser; or a Ti:sapphire lasercan be continuously oscillated. Further, pulse oscillation thereof canbe performed with an oscillation frequency of 10 MHz or more by carryingout Q switch operation, mode synchronization, or the like. When a laserbeam is oscillated with a repetition rate of 10 MHz or more, asemiconductor film is irradiated with a next pulse during thesemiconductor film is melted by the laser beam and then is solidified.Therefore, differing from a case of using a pulse laser with a lowrepetition rate, a solid-liquid interface can be continuously moved inthe semiconductor film so that crystal grains, which continuously growtoward a scanning direction, can be obtained.

When ceramic (polycrystal) is used as a medium, the medium can be formedto have a free shape for short time at low cost. When using a singlecrystal, a columnar medium with several mm in diameter and several tensof mm in length is usually used. In the case of using the ceramic, amedium bigger than the case of using the single crystal can be formed.

A concentration of a dopant such as Nd or Yb in a medium, which directlycontributes to light emission, cannot be changed largely in both casesof the single crystal and the polycrystal; therefore, there is a limitin improvement in output of a laser by increasing the concentration tosome extent. However, in the case of the ceramic, the size of a mediumcan be significantly increased as compared with the case of the singlecrystal, and therefore, drastic improvement in output of a laser can beexpected.

Further, in the case of the ceramic, a medium with a parallel six-hedronshape or a cuboid shape can be easily formed. In a case of using amedium having such a shape, when oscillated light is made travel inzigzag inside of the medium, a long path of the oscillated light can beobtained. Therefore, amplitude is increased and a laser beam can beoscillated at high output. Furthermore, a cross sectional shape of alaser beam emitted from a medium having such a shape is a quadrangularshape, and therefore, as compared with a laser beam with a circularshape, the laser beam with the quadrangular shape in cross section havean advantage to be shaped into a linear beam. By shaping a laser beamemitted in the above described manner using an optical system, a linearbeam with 1 mm or less in length of a short side and several mm toseveral m in length of a long side can be easily obtained. In addition,when a medium is uniformly irradiated with excited light, a linear beamis emitted with a uniform energy distribution in a long side direction.Further, it is preferable that a semiconductor film be irradiated withlaser at an incident angle θ (0<θ<90°); thereby an interference of thelaser can be prevented.

By irradiating the semiconductor film with this linear beam, the entiresurface of the semiconductor film can be more evenly annealed. When thelinear beam is required to be even to the opposite ends, slits areprovided at the opposite ends to shield light of energy attenuationportions or other measures are required to be taken.

The semiconductor film obtained in this manner is annealed with thelinear beam having uniform intensity, and a semiconductor device ismanufactured by using the semiconductor film. Then, the characteristicof the semiconductor device can be favorable and uniform.

Further, the semiconductor film may be irradiated with the laser beam inthe atmosphere of an inert gas such as a rare gas or nitrogen.Accordingly, roughness of the surface of the semiconductor can besuppressed by an irradiation of the laser beam, and variation of athreshold value generated by variation of interface state density can besuppressed.

An amorphous semiconductor film may be crystallized by the combinationof thermal treatment and laser light irradiation, or one of thermaltreatment and laser light irradiation may be performed a plurality oftimes.

In this embodiment mode, an amorphous semiconductor film is formed overthe base film 101 b and the amorphous semiconductor film is crystallizedto form a crystalline semiconductor film. As the amorphous semiconductorfilm, amorphous silicon formed using a reaction gas of SiH₄ and H₂ isused. In this embodiment mode, the base film 101 a, the base film 101 b,and the amorphous semiconductor film are continuously formed by changinga reaction gas without breaking the vacuum in the same chamber at thesame temperature of 330° C.

After removing an oxide film formed over the amorphous semiconductorfilm, an oxide film is formed with a thickness of 1 to 5 nm by UV lightirradiation in an oxygen atmosphere, a thermal oxidization method,treatment with ozone water or hydrogen peroxide including hydroxylradical, or the like. In this embodiment mode, Ni is used as an elementfor promoting crystallization. An aqueous solution containing 10 ppm ofNi acetate is applied by a spin coating method.

In this embodiment mode, after performing thermal treatment at 750° for3 minutes by an RTA method, the oxide film formed over the semiconductorfilm is removed and laser light irradiation is applied. The amorphoussemiconductor film is crystallized by the aforementioned crystallizationtreatment to be a crystalline semiconductor film.

In the case of performing crystallization using a metal element, agettering step is performed for reducing or removing the metal element.In this embodiment mode, the metal element is captured using theamorphous semiconductor film as a gettering sink. First, an oxide filmis formed over the crystalline semiconductor film by UV lightirradiation in an oxygen atmosphere, a thermal oxidation method,treatment with ozone water or hydrogen peroxide including hydroxylradical, or the like. It is desirable that the oxide film be formedthicker by heat treatment. Subsequently, an amorphous semiconductor filmis formed with a thickness of 50 nm by a plasma CVD method (with acondition of this embodiment mode as 350 W, 35 Pa, deposition gas: SiH₄(flow rate of 5 sccm) and Ar (flow rate 1000 sccm)).

After that, thermal treatment is performed at 744° C. for three minutesby an RTA method to reduce or remove the metal element. The thermaltreatment may be performed in a nitrogen atmosphere. Then, the amorphoussemiconductor film as a gettering sink and an oxide film formed over theamorphous semiconductor film are removed with hydrofluoric acid and thelike, thereby a crystalline semiconductor film 102 in which the metalelement is reduced or removed can be obtained (see FIG. 5A). In thisembodiment mode, the amorphous semiconductor film as a gettering sink isremoved using TMAH (Tetramethyl ammonium hydroxide).

The semiconductor film obtained in this manner may be doped with aslight amount of impurity element (boron or phosphorus) for controllinga threshold voltage of a thin film transistor. This doping of impurityelement may be performed to an amorphous semiconductor film before acrystallization step. When impurity element are doped in a state of theamorphous semiconductor film, the impurity can be activated by heattreatment for crystallization later. Further, a defect and the likegenerated at the doping can be improved as well.

Subsequently, the crystalline semiconductor film 102 is processed into adesired shape. In this embodiment mode, after removing the oxide filmformed over the crystalline semiconductor film 102, an oxide film isnewly formed. Then, the oxide film is etched into a desired shape;thereby a semiconductor layer 103, a semiconductor layer 104, asemiconductor layer 105, and a semiconductor layer 106 are formed.

An etching process may adopt either plasma etching (dry etching) or wetetching. However, in the case of processing a large area substrate,plasma etching is suitable. As an etching gas, a gas containing fluorinesuch as CF₄ and NF₃ or a gas containing chlorine such as Cl₂ and BCl₃ isused, to which an inert gas such as He and Ar may be appropriatelyadded. Further, in the case of applying an etching process byatmospheric pressure discharge, local discharge can be realized, therebya mask layer is not required to be formed over an entire surface of thesubstrate.

In the invention, a conductive layer for forming a wiring layer or anelectrode layer, a mask layer for forming a predetermined pattern, orthe like may be formed by a method where a pattern can be selectivelyformed such as a droplet discharge method. In the droplet discharge(ejecting) method (also referred to as an inkjet method depending on thesystem thereof), a predetermined pattern (a conductive layer, aninsulating layer, and the like) can be formed by selectively discharging(ejecting) droplets of a composition prepared for a specific purpose. Atthis time, a process for controlling wettability and adhesion may beperformed to a region for forming a pattern. Additionally, a method fortransferring or drawing a pattern, for example, a printing method (amethod for forming a pattern such as screen printing and offsetprinting) or the like can be used.

In this embodiment mode, a resin material such as an epoxy resin, anacrylic resin, a phenol resin, a novolac resin, a melamine resin, or aurethane resin is used for a mask to be used. Alternatively, the maskmay be formed using an organic material such as benzocyclobutene,parylene, fluorinated arylene ether and polyimide having a lighttransmitting property; a compound material formed by polymerization ofsiloxane polymers or the like; a composition material containing awater-soluble homopolymer and a water-soluble copolymer; and the like.In addition, a commercially available resist material containing aphotosensitive agent may also be used. For example, a novolac resin anda naphthoquinonediazide compound that is a photosensitive agent, whichare typical positive type resist; a base resin that is a negative typeresist, diphenylsilanediol, an acid generating material, and the likemay be used. In the case where a droplet discharge method is used, evenwhen any material is used, the surface tension and the viscosity areappropriately adjusted by controlling the solvent concentration, addinga surfactant, or the like.

The oxide film over the semiconductor layer is removed to form a gateinsulating layer 107 covering the semiconductor layer 103, thesemiconductor layer 104, the semiconductor layer 105, and thesemiconductor layer 106. The gate insulating layer 107 is formed of aninsulating film containing silicon with a thickness of 10 to 150 nmusing a plasma CVD method or a sputtering method. The gate insulatinglayer 107 may be formed of a known material such as an oxide material ornitride material of silicon, typified by silicon nitride, silicon oxide,silicon oxynitride, and silicon nitride oxide and may be stacked layersor a single layer. Three stacked layers of a silicon nitride film, asilicon oxide film, and a silicon nitride film are used for the gateinsulating layer. Alternatively, a single layer or stacked layers of twolayers of the aforementioned film or a silicon oxynitride film may beemployed as well. Furthermore, a thin silicon oxide film may be formedbetween the semiconductor layer and the gate insulating layer with athickness of 1 to 100 nm, preferably 1 to 10 nm, and more preferably 2to 5 nm. As a method for forming the thin silicon oxide film, thesurface of the semiconductor region is oxidized by a GRTA method, anLRTA method, or the like to form a thermal oxide film is formed, therebya silicon oxide film with a thin thickness can be formed. Note that arare gas element such as argon may be contained in a reaction gas so asto be mixed into an insulating film to be formed in order to form adense insulating film having a little gate leak current at low filmdeposition temperature.

Subsequently, a first conductive film 108 with a thickness of 20 to 100nm and a second conductive film 109 with a thickness of 100 to 400 nm,each of which is used as a gate electrode layer are stacked over thegate insulating layer 107 (see FIG. 5B). The first conductive film 108and the second conductive film 109 can be formed by a known method suchas a sputtering method, a vapor deposition method, or a CVD method. Thefirst conductive film 108 and the second conductive film 109 may beformed of an element selected from tantalum (Ta), tungsten (W), titanium(Ti), molybdenum (Mo), aluminum (Al), copper (Cu), chromium (Cr), andneodymium (Nd), or an alloy material or compound material having theaforementioned element as a main component. Moreover, a semiconductorfilm typified by a polycrystalline silicon film which is doped withimpurity element such as phosphorus or an AgPdCu alloy may be used asthe first conductive film 108 and the second conductive film 109.Further, the conductive film is not limited to the two-layer structure,and for example, may have a three-layer structure in which a tungstenfilm with a thickness of 50 nm as a first conductive film, an alloy filmof aluminum and silicon (Al—Si) with a thickness of 500 nm as a secondconductive film, and a titanium nitride film with a thickness of 30 nmas the third conductive film are sequentially stacked. Moreover, in thecase of the three-layer structure, tungsten nitride may be used insteadof tungsten as the first conductive film; an alloy film of aluminum andtitanium (Al—Ti) may be used instead of the alloy film of aluminum andsilicon (Al—Si) as the second conductive film; or a titanium film may beused instead of the titanium nitride film as the third conductive film.In this embodiment mode, tantalum nitride (TaN) is formed with athickness of 30 nm as the first conductive film 108 and tungsten (W) isformed with a thickness of 370 nm as the second conductive film 109.

Mask layers 157 a, 157 b, 157 c, 157 d, and 157 e of resists forprocessing into desired shapes are formed over the gate insulating layer107, the first conductive film 108, and the second conductive film 109(see FIG. 5C). The mask layers 157 a, 157 b, 157 c, 157 d, and 157 e areformed by using an exposure mask provided with a diffraction gratingpattern or an auxiliary pattern formed of a semi-transmissive film witha light intensity reducing function similarly to the mask layers 306,366 a, 366 b, and 366 c described in Embodiment Modes 1 and 4. With suchan exposure mask, various light exposures can be more accuratelycontrolled, which enables a resist to be processed into a more accurateshape. Therefore, when such a mask layer is used, the conductive filmand the insulating film can be processed in the same step into differentshapes in accordance with desired performances. As a result, thin filmtransistors with different characteristics, wires in different sizes andshapes, and the like can be manufactured without increasing the numberof steps.

Next, the first conductive layer 108 and the second conductive layer 109are etched into desired shapes by using the mask layers 157 a, 157 b,157 c, 157 d, and 157 e, thereby first gate electrode layers 121, 122,124, 125, and 126, and second gate electrode layers 131, 132, 134, 135,and 136 are formed (see FIG. 5D). By the step of etching the firstconductive film 108 and the second conductive film 109, the mask layers157 a, 157 b, 157 c, 157 d, and 157 e are etched to be mask layers 110a, 110 b, 110 c, 110 d, and 110 e and removed later.

As an etching method, a plasma etching method, a reactive ion etchingmethod, and an ICP (Inductively Coupled Plasma) etching method can beused. In this embodiment mode, an ICP etching method is used. Theetching conditions (amount of power applied to a coil type electrodelayer, amount of power applied to an electrode layer on the substrateside, an electrode temperature on the substrate side, or the like) maybe appropriately controlled. The etching step may be performed aplurality of times or once as in this embodiment mode. As the etchinggas, a gas containing chlorine typified by Cl₂, BCl₃, SiCl₄, CCl₄, orthe like, a gas containing fluorine typified by CF₄, CF₅, SF₆, NF₃, orthe like, or O₂ can be appropriately used. In this embodiment mode, thegate electrode layer is formed by dry etching but wet etching may alsobe employed.

In this embodiment mode, the first gate electrode layers and the secondgate electrode layers have tapered shapes. However, the invention is notlimited to this and only one side of the gate electrode layer may have atapered shape while the other side may have a perpendicular sidesurface. As described in this embodiment mode, a taper angle may bedifferent or the same between the stacked gate electrode layers. Withthe tapered shape, coverage of a film stacked thereover is improved anddefects are reduced, which improves reliability. The shape of the gateelectrode layer such as the tapered shape can be controlled finely andaccurately by using a resist mask formed by the exposure process shownin FIGS. 19A and 19B as in this embodiment mode.

The gate insulating layer 107 is etched to some degree by the etchingstep of forming the gate electrode layer and a thickness thereof isreduced (what is called film reduction) in some cases.

Next, a mask layer 153 a covering the first gate electrode layer 121,the second gate electrode layer 131, and the semiconductor layer 103,and a mask layer 153 b covering the first gate electrode layer 126, thesecond gate electrode layer 136, and the semiconductor layer 106 areformed. Then, an impurity element imparting one conductivity type isintroduced to the semiconductor layers 104 and 105 to form impurityregions. In a step shown in FIG. 6A, an impurity element impartingn-type conductivity (phosphorus (P) in this embodiment mode) is used asan impurity element imparting one conductivity type in order to form ann-channel thin film transistor.

An impurity element 152 imparting n-type conductivity is added to thesemiconductor layer 104 over which the first gate electrode layer 122and the second gate electrode layer 132 are provided and thesemiconductor layer 105 over which the first gate electrode layer 124,the first gate electrode layer 125, the second gate electrode layer 134,and the second gate electrode layer 135 are provided, thereby firstn-type impurity regions 145 a, 145 b, 148 a, 148 b, 148 c, and 148 d,and second n-type impurity regions 144 a, 144 b, 147 a, 147 b, and 147 care formed (see FIG. 6A). The semiconductor layers 104 and 105 ofregions to which the impurity element 152 is not added correspond tochannel forming regions 146, 149 a, and 149 b. It is to be noted thatthe semiconductor layers 103 and 106 are protected by the mask layer 153a and 153 b from the impurity element 152.

The second n-type impurity regions 144 a, 144 b, 147 a, 147 b, and 147 cformed by adding the impurity element 152 imparting n-type conductivityto the semiconductor layer 104 and 105 of regions which are not coveredwith the first gate electrode layers 122, 124, and 125, and the secondgate electrode layers 132, 134, and 135 correspond to high concentrationn-type impurity regions. On the other hand, the first n-type impurityregions 145 a, 145 b, 148 a, 148 b, 148 c, and 148 d formed by addingthe impurity element 152 imparting n-type conductivity to thesemiconductor layer 104 and 105 through the first gate electrode layers122, 124, and 125 of regions which are not covered with the second gateelectrode layer 132, 134, and 135 correspond to low concentration n-typeimpurity regions.

In this embodiment mode, the gate electrode layer has a stacked-layerstructure. By utilizing the different shapes of the first gate electrodelayers 122, 124, and 125 and the second gate electrode layers 132, 134,and 135, the first n-type impurity regions 145 a, 145 b, 148 a, 148 b,148 c, and 148 d, the second n-type impurity regions 144 a, 144 b, 147a, 147 b, and 147 c are formed in a self-aligned manner by adding theimpurity element 152 imparting n-type conductivity once.

Each impurity region may be formed by adding the impurity element 152imparting n-type conductivity a plurality of times or once. Bycontrolling doping conditions to add the impurity element, whetherimpurity regions with different concentrations are formed by once or aplurality of adding steps can be selected.

The second n-type impurity regions 144 a, 144 b, 147 a, 147 b, and 147 cwhich are high concentration n-type impurity regions function as sourceregions and drain regions. On the other hand, the first n-type impurityregions 145 a, 145 b, 148 a, 148 b, 148 c, and 148 d which are lowconcentration n-type impurity regions function as LDD regions. In thisembodiment mode, the first n-type impurity regions 145 a and 145 b whichare covered with the first gate electrode layer 122 with the gateinsulating layer 107 interposed therebetween are Lov regions which canalleviate an electric field in the vicinity of the drain region toprevent deterioration of an on current caused by hot carrier injection.As a result, a thin film transistor capable of high speed operation canbe formed.

In this embodiment mode also, an impurity region overlapped with a gateelectrode layer with a gate insulating layer interposed therebetween isexpressed as a Lov region while an impurity region which is notoverlapped with a gate electrode layer with a gate insulating layerinterposed therebetween is expressed as a Loff region. In FIGS. 6A and6B, the impurity regions are expressed by hatching and white, which doesnot mean that an impurity element is not added to the white portion.They are expressed like this so that it is easily recognized that theconcentration distribution of impurity elements in this region reflectsconditions of mask or doping. It is to be noted that this is similar inthe other drawings of this specification.

In this embodiment mode, PH₃ (PH₃ is diluted with hydrogen (H) by 5% asa doping gas) is used as a doping gas containing an impurity element,and the doping is conducted with the conditions of a gas flow rate of 80sccm, a beam current of 540 μA/cm, an accelerating voltage of 70 kV, anda dose amount of 5.0×10¹⁵ ions/cm². The impurity element impartingn-type conductivity is contained in the first n-type impurity regions145 a, 145 b, 148 a, 148 b, 148 c, and 148 d at a concentration of about1×10¹⁷ to 5×10¹⁸/cm³. The impurity element imparting n-type conductivityis contained in the second n-type impurity regions 144 a, 144 b, 147 a,147 b, and 147 c at a concentration of about 5×10¹⁹ to 5×10²⁰/cm³.

The mask layers 153 a and 153 b are removed and a mask layer 155 acovering the first gate electrode layer 122, the second gate electrodelayer 132, and the semiconductor layer 103, and a mask layer 155 bcovering the first gate electrode layers 124 and 125, the second gateelectrode layers 134 and 135, and the semiconductor layer 105 areformed. An impurity element imparting p-type conductivity (in thisembodiment mode, boron (B)) is added as an impurity element impartingone conductivity type to the semiconductor layers 103 and 106, therebyimpurity regions are formed. In this embodiment mode, an impurityelement 154 imparting p-type conductivity is added to the semiconductorlayer 103 over which the first gate electrode layer 121 and the secondgate electrode layer 131 are provided and the semiconductor layer 106over which the first gate electrode layer 126 and the second gateelectrode layer 136 are provided, thereby first p-type impurity regions161 a, 161 b, 164 a, and 164 b, and second p-type impurity regions 160a, 160 b, 163 a, and 163 b are formed (see FIG. 6B). The semiconductorlayer 103 or 106 of a region to which the impurity element 154 is notadded becomes a channel forming region 162 or 165. It is to be notedthat the semiconductor layers 104 and 105 are protected by the masklayers 155 a and 155 b from the impurity element 154.

The second p-type impurity regions 160 a, 160 b, 163 a, and 163 b formedby adding the impurity element 154 imparting p-type conductivity to thesemiconductor layers 103 and 106 of regions which are not covered withthe first gate electrode layers 121 and 126, and the second gateelectrode layers 131 and 136 correspond to high concentration p-typeimpurity regions. On the other hand, the first p-type impurity regions161 a, 161 b, 164 a, and 164 b formed by adding the impurity element 154imparting p-type conductivity to the semiconductor layers 103 and 106through the first gate electrode layers 121 and 126 of regions which arenot covered with the second gate electrode layers 131 and 136 correspondto low concentration p-type impurity regions.

Each impurity region may be formed by adding the impurity element 154imparting p-type conductivity to the semiconductor layers 103 and 106 aplurality of times or once. In this embodiment mode, the first p-typeimpurity regions 161 a, 161 b, 164 a, and 164 b have lowerconcentrations of impurity element imparting p-type conductivity thanthe second p-type impurity regions 160 a, 160 b, 163 a, and 163 b,however, depending on the conditions of adding the impurity element, theimpurity regions under the first gate electrode layers 121 and 126 havehigher concentrations of impurity element than the impurity regionswhich are not covered with the first gate electrode layers 121 and 126in some cases. Therefore, there is a case where the first p-typeimpurity regions 161 a, 161 b, 164 a, and 164 b have concentrations ofimpurity element imparting p-type conductivity higher than orapproximately equal to the second p-type impurity regions 160 a, 160 b,163 a, and 163 b.

In this embodiment mode, boron (B) is used as an impurity element,therefore, diborane (B₂H₆) is used as a doping gas (B₂H₆ is diluted withhydrogen (H₂) by 15% as doping gas) containing an impurity element fordoping at a gas flow rate of 70 sccm, with a beam current of 180 μA/cm,an acceleration voltage of 80 kV, and a dosage of 2.0×10¹⁵ ions/cm². Animpurity element imparting p-type conductivity is added to the secondp-type impurity regions 160 a, 160 b, 163 a, and 163 b at aconcentration of about 1×10²⁰ to 5×10²¹/cm³. The impurity elementimparting p-type conductivity is added to the first p-type impurityregions 161 b, 164 a, and 164 b at a concentration of about 5×10¹⁸ to5×10¹⁹/cm³. In this embodiment mode, the first p-type impurity regions161 a, 161 b, 164 a, and 164 b are formed so as to have lowerconcentrations than the second p-type impurity regions 160 a, 160 b, 163a, and 163 b in a self-aligned manner, which reflect the shapes of thefirst gate electrode layers 121 and 126, and the second gate electrodelayers 131 and 136.

The second p-type impurity regions 160 a, 160 b, 163 a, and 163 b whichare high concentration p-type impurity regions function as sourceregions and drain regions. On the other hand, the first p-type impurityregions 161 a, 161 b, 164 a, and 164 b which are low concentrationp-type impurity regions function as LDD regions. The first p-typeimpurity regions 161 a, 161 b, 164 a, and 164 b which are covered withthe first gate electrode layers 121 and 126 with the gate insulatinglayer 107 interposed therebetween are Lov regions, which can alleviatean electric field in the vicinity of the drain region.

A mask layer 156 a covering the first gate electrode layer 121, thesecond gate electrode layer 131, the semiconductor layer 103, the firstgate electrode layer 122, the second gate electrode layer 132, and thesemiconductor layer 104, and a mask layer 156 b covering the first gateelectrode layer 126, the second gate electrode layer 136, and thesemiconductor layer 106 are formed, and the first gate electrode layers124 and 125 are etched by using the second gate electrode layers 134 and135 as masks, thereby a first gate electrode layer 120 a and a firstgate electrode layer 120 b are formed (see FIG. 7A). The first gateelectrode layers 120 a and 120 b have shapes in which regions thereofwhich extend to exist outside the second gate electrode layer 134 andthe second gate electrode layer 135 are removed, which reflect theshapes of the second gate electrode layer 134 and the second gateelectrode layer 135. Therefore, edge portions of the first gateelectrode layer 120 a and the second gate electrode layer 134 and thoseof the first gate electrode layer 120 b and the second gate electrodelayer 135 almost correspond to each other.

As the first gate electrode layers 120 a and 120 b are formed, the firstn-type impurity regions 148 a, 148 b, 148 c, and 148 d are formed asLoff regions which are not covered with the first gate electrode layers120 a and 120 b with the gate insulating layer 107 interposedtherebetween. The first n-type impurity region 148 a, 148 b, 148 c, or148 d as a Loff region on a drain side has effects to alleviate anelectric field in the vicinity of the drain to prevent deteriorationcaused by hot carrier injection and to reduce an off current. As aresult, a semiconductor device with high reliability and low powerconsumption can be manufactured.

The mask layers 156 a and 156 b are removed by O₂ ashing or a resistpeeling solution.

In order to activate an impurity element, thermal treatment orirradiation of intense light or laser light may be carried out. At thesame time as the activation, plasma damage to the gate insulating layeror an interface between the gate insulating layer and the semiconductorlayer can be improved.

Then, a first interlayer insulating layer covering the gate electrodelayers and the gate insulating layer is formed. In this embodiment mode,the first interlayer insulating layer has a stacked-layer structure ofinsulating films 167 and 168 (see FIG. 7B). A silicon nitride oxide filmis formed with a thickness of 200 nm as the insulating film 167 and asilicon oxynitride film is formed with a thickness of 800 nm as theinsulating film 168, which are stacked. A three-layer structure coveringthe gate electrode layer and the gate insulating layer, constituted by asilicon oxynitride film formed with a thickness of 50 nm, a siliconnitride oxide film formed with a thickness of 140 nm, and a siliconoxynitride film formed with a thickness of 800 nm may also be employed.In this embodiment mode, the insulating films 167 and 168 arecontinuously formed by a plasma CVD method similarly to the base film.The insulating films 167 and 168 can be formed of a silicon nitridefilm, a silicon nitride oxide film, a silicon oxynitride film, a siliconoxide film, or the like by a sputtering method or a plasma CVD method,or a single layer or a stacked-layer structure of three or more layersof other insulating films containing silicon.

Further, thermal treatment is performed at 300 to 550° C. for 1 to 12hours in a nitrogen atmosphere to hydrogenate the semiconductor layer.The temperature is preferably 400 to 500° C. This step is carried outfor terminating dangling bonds in the semiconductor layer by hydrogencontained in the insulating film 167 which is an interlayer insulatinglayer. In this embodiment mode, the thermal treatment is carried out at410° C.

As the insulating films 167 and 168, a material selected from aluminumnitride (AlN), aluminum oxynitride (AlON), aluminum nitride oxide (AlNO)containing more nitrogen than oxygen, aluminum oxide, diamond-likecarbon (DLC), nitrogen-containing carbon (CN), polysilazane, or othersubstances containing an inorganic insulating material can be used.Alternatively, siloxane resin may be used. Further, an organicinsulating material may be used, such as polyimide, acrylic, polyamide,polyimide amide, resist, or benzocyclobutene. Moreover, oxazole resincan also be used, which is, for example, photosensitive polybenzoxazole.Photosensitive polybenzoxazole has a low dielectric constant (adielectric constant of 2.9 at a normal temperature at 1 MHz), high heatresistance (TGA: Thermal Gravity Analysis) thermal decompositiontemperature of 550° C. with the rise in temperature at 5° C./min), andlow moisture absorbing rate (0.3% in 24 hours at a normal temperature).A coating film formed by a coating method with favorable planarity mayalso be used.

Next, contact holes (openings) reaching the semiconductor layer areformed in the insulating films 167 and 168, and the gate insulatinglayer 107 by using a mask of resist. Etching may be performed once or aplurality of times depending on a selection ratio of a material to beused. The insulating films 168, 167, and the gate insulating layer 107are removed and openings reaching the second p-type impurity regions 160a, 160 b, 163 a, and 163 b, and the second n-type impurity regions 144a, 144 b, 147 a, and 147 b are formed. Etching may be performed by wetetching, dry etching, or both of them. As the etching gas, a gascontaining chlorine typified by Cl₂, BCl₃, SiCl₄, CCl₄, or the like, agas containing fluorine typified by CF₄, SF₆, NF₃, or the like, or O₂can be appropriately used. It is possible to add an inert gas to theetching gas. As an inert element to be added, one or a plurality ofelements selected from He, Ne, Ar, Kr, and Xe can be used.

A conductive film is formed so as to cover the openings, and theconductive film is etched to form source electrode layers or drainelectrode layers 169 a, 169 b, 170 a, 170 b, 171 a, 171 b, 172 a, and172 b which are electrically connected to portions of respective sourceregions or drain regions. The source electrode layers and drainelectrode layers can be formed by depositing conductive films by a PVDmethod, a CVD method, a vapor deposition method, or the like and thenetching them into desired shapes. Furthermore, a conductive layer can beselectively formed at a predetermined position by a droplet dischargemethod, a printing method, an electrolytic plating method, or the like.In addition, a reflow method, a damascene method, or the like may alsobe employed. The source electrode layers or drain electrode layers areformed of a metal such as Ag, Au, Cu, Ni, Pt, Pd, Ir, Rh, W, Al, Ta, Mo,Cd, Zn, Fe, Ti, Si, Ge, Zr, or Ba, an alloy or a metal nitride thereof.A stacked-layer structure of the aforementioned substances may also beused. In this embodiment mode, a titanium (Ti) film is formed with athickness of 100 nm, an alloy of aluminum and silicon (Al—Si) is formedwith a thickness of 700 nm, and titanium (Ti) is formed with a thicknessof 200 nm, which are then processed into desired shapes.

By the aforementioned steps, an active matrix substrate can be formed,which includes a p-channel thin film transistor 173 having a p-typeimpurity region in a Lov region and an n-channel thin film transistor174 having an n-type impurity region in a Lov region in a peripheraldriver circuit region 204, a multi-channel type n-channel thin filmtransistor 175 having an n-type impurity region in a Loff region and ap-channel thin film transistor 176 having a p-type impurity region in aLov region in a pixel region 206 (see FIG. 7C).

The active matrix substrate can be used for a light emitting deviceincluding a self-luminous element, a liquid crystal display deviceincluding a liquid crystal element, and other display devices. Further,the active matrix substrate can be applied to various processorstypified by a CPU (Central Processing Unit) or a semiconductor devicesuch as a card incorporating an ID chip.

The structure of the thin film transistor is not limited to thisembodiment mode, and may be a single gate structure having one channelforming region, a double gate structure having two channel formingregions, or a triple gate structure having three channel formingregions. Moreover, a thin film transistor in the peripheral drivercircuit region may have a single gate structure, a double gatestructure, or a triple gate structure.

Next, insulating films 181 and 182 are formed as second interlayerinsulating layers (see FIG. 8A). FIGS. 8A and 8B show manufacturingsteps of a display device, including a separating region 201 forseparating the substrate by scribing, an external terminal connectingregion 202 as an attaching portion of an FPC, a wiring region 203 as aperipheral wire leading region, a peripheral driver circuit region 204,and a pixel region 206. The wiring region 203 is provided with wires 179a and 179 b and the external terminal connecting region 202 is providedwith a terminal electrode layer 178 connected to an external terminal.

The insulating films 181 and 182 can be formed of a material selectedfrom silicon oxide, silicon nitride, silicon oxynitride, silicon nitrideoxide, aluminum nitride (AlN), aluminum oxide containing nitrogen (alsocalled aluminum oxynitride) (AlON), aluminum nitride containing oxygen(also called aluminum nitride oxide) (AlNO), aluminum oxide,diamond-like carbon (DLC), a nitrogen-containing carbon film (CN), PSG(phosphosilicate glass), BPSG (borophosphosilicate glass), an aluminafilm, or other substances containing an inorganic insulating material.Alternatively, siloxane resin may also be used. Further, an organicinsulating material may be used, which may be a photosensitive type or anon-photosensitive type, such as polyimide, acrylic, polyamide,polyimide amide, resist, benzocyclobutene, polysilazane, or a lowdielectric constant (Low-k) material. Moreover, oxazole resin can alsobe used, which is, for example, photosensitive polybenzoxazole.Photosensitive polybenzoxazole has a low dielectric constant (adielectric constant of 2.9 at a normal temperature at 1 MHz), high heatresistance (TGA: Thermal Gravity Analysis) thermal decompositiontemperature of 550° C. with the rise in temperature at 5° C./min), andlow moisture absorbing rate (0.3% in 24 hours at a normal temperature).

An interlayer insulating layer provided for planarization is required tobe high in heat resistance, an insulating property, and a planarizingproperty. Therefore, a coating method typified by a spin coating methodis preferably used for forming the insulating film 181. In thisembodiment mode, the insulating film 181 is formed of a coated filmusing a siloxane resin material while the insulating film 182 is formedof a silicon nitride oxide film by a CVD method.

The insulating films 181 and 182 can be formed by a dipping method,spray coating, a doctor knife, a roll coater, a curtain coater, a knifecoater, a CVD method, a vapor deposition method, or the like. Theinsulating films 181 and 182 may be formed by a droplet dischargemethod. In the case of using a droplet discharge method, a materialsolution can be used economically. Moreover, a method enabling a patternto be transferred or drawn such as a droplet discharge method, forexample, a printing method (a method to form a pattern such as screenprinting or offset printing) can also be used.

As shown in FIG. 8B, openings are formed in the insulating films 181 and182 which are interlayer insulating layers. The insulating films 181 and182 are required to be etched in a wide area in a connecting region 205(see FIG. 10A), the peripheral driver circuit region 204, the wiringregion 203, the external terminal connecting region 202, the separatingregion 201, and the like. The connecting region 205 is a region shown inthe top plan view of FIG. 10A, where a wiring layer manufactured in thesame step as the source electrode layer or the drain electrode layer anda second electrode layer which later functions as an upper electrodelayer of a light emitting element are electrically connected. Theconnecting region 205 is omitted in FIGS. 8A and 8B. Therefore, anopening is required to be formed in the insulating films 181 and 182 inthe connecting region 205 as well. However, the opening area of thepixel region 206 is much smaller and finer than the opening area of theperipheral driver circuit region 204 or the like. Therefore, a margin ofthe etching conditions can be expanded by providing a photolithographystep for forming the opening in the pixel region and a photolithographystep for forming an opening in the connecting region. As a result, yieldcan be improved. Moreover, when the margin of etching conditions isexpanded, a contact hole can be formed in the pixel region at highprecision.

In specific, an opening of a wide area is formed in the insulating films181 and 182 provided in the connecting region 205, the peripheral drivercircuit region 204, the wiring region 203, the external terminalconnecting region 202, and the separating region 201. For forming theopening, a mask is formed to cover the insulating films 181 and 182 inthe non-opening region in the pixel region 206, the connecting region205, the peripheral driver circuit region 204, the wiring region 203,and the external terminal connecting region 202. A parallel plate RIEapparatus or an ICP etching apparatus can be used for etching. Etchingis preferably performed until the wiring layer or the insulating film168 is over-etched. By over-etching the films in this manner, variationsin film thickness and etching rate in the substrate can be reduced. Inthis manner, openings are formed in the connecting region 205, theperipheral driver circuit region 204, the wiring region 203, theexternal terminal connecting region 202, and the separating region 201.An opening 183 is formed in the external terminal connecting region 202,thereby a terminal electrode layer 178 is exposed.

After that, a fine opening, which is a contact hole, is formed in theinsulating films 181 and 182 of the pixel region 206. At this time, amask is formed to cover the insulating films 181 and 182 in thenon-opening region of the pixel region 206, and the connecting region205, the peripheral driver circuit region 204, the wiring region 203,and the external terminal connecting region 202. The mask is used forforming the opening in the pixel region 206 and is provided with a fineopening at a predetermined position. As such a mask, for example, aresist mask can be used.

By using the parallel plate RIE apparatus, the insulating films 181 and182 are etched. It is to be noted that etching is preferably performeduntil the wiring layer and the insulating film 168 are over-etched. Byover-etching the films in this manner, variations in film thickness andetching rate in the substrate can be reduced.

Moreover, an ICP apparatus may also be used as the etching apparatus. Bythe aforementioned steps, an opening 184 to reach the source electrodelayer or drain electrode layer 172 b is formed in the pixel region 206(see FIG. 8B).

Etching for forming the opening may be performed a plurality of times atthe same position. For example, the opening in the connecting region 205having a wide area requires to be etched a lot. Such a wide area openingmay be formed by performing etching a plurality of times. Moreover,etching may be similarly performed a plurality of times in the case offorming an opening deeper than other openings.

In this embodiment mode, the openings are formed in the insulating films181 and 182 with a plurality of steps separately; however, they may beformed by one etching step as well. In this case, etching is performedwith an ICP power of 7000 W, a bias power of 1000 W, and a pressure of0.8 Pascal (Pa), using an etching gas including 2400 sccm of CF₄ and 160sccm of O₂ by using an ICP apparatus. A bias power is preferably 1000 to4000 W. The openings are formed by one etching step; therefore, it isadvantageous in that the manufacturing steps can be simplified.

In the case of forming all the openings in the insulating films 181 and182 in one step, it is preferable to use a mask layer formed of anexposure mask provided with a diffraction grating pattern or anauxiliary pattern formed of a semi-transmissive film having a lightintensity reducing function. With such an exposure mask, a mask layerhaving regions with different thicknesses can be formed. That is, it ispossible to form a mask layer thick in a region where the opening isshallow such as the opening 184 and form a mask layer thin in a regionwhere the opening is deep such as the opening 183. When a mask layerhaving a gradient in thickness by the desired depth of etching is used,different depths of etching can be performed by one etching step.Therefore, in the shallow opening, as exposed wiring layer or the likeis not exposed to etching treatment for a long time, damage to thewiring layer by a lot of over-etching can be prevented.

Next, a first electrode layer 185 (also called a pixel electrode layer)is formed so as to contact the source electrode layer or the drainelectrode layer 172 b. The first electrode layer functions as an anodeor a cathode and is formed of a film containing as a main component anelement selected from Ti, Ni, W, Cr, Pt, Zn, Sn, In, or Mo, an alloymaterial or a compound material containing the aforementioned element asa main component, such as TiN, TiSi_(x)N_(y), WSi_(x), WN_(x),WSi_(x)N_(y), and NbN, or a stacked-layer of these with a totalthickness of 100 to 800 nm.

In this embodiment mode, a light emitting element is used as a displayelement and light emitted from the light emitting element is extractedfrom the first electrode layer 185 side. Therefore, the first electrodelayer 185 has light transmittance. As the first electrode layer 185, atransparent conductive film is formed and etched into a desired shape(see FIG. 9A). In this embodiment mode, by forming a transparentconductive film in a desired shape over the insulating film 182, theinsulating film 182 functions as an etching stopper as well when thefirst electrode layer 185 is etched.

In the invention, a transparent conductive film formed of a conductivematerial having light transmittance is preferably used in the firstelectrode layer 185 as a light transmissive electrode layer, for whichindium oxide containing tungsten oxide, indium zinc oxide containingtungsten oxide, indium oxide containing titanium oxide, indium tin oxidecontaining titanium oxide, or the like can be used. It is needless tosay that indium tin oxide (ITO), indium zinc oxide (IZO), indium tinoxide to which silicon oxide is added (ITSO), or the like can also beused.

An example of composition ratio of a conductive material having lighttransmissivity is described. The composition ratio of indium oxidecontaining tungsten oxide is preferably 1.0 wt %:99.0 wt %=tungstenoxide:indium oxide. The composition ratio of indium zinc oxidecontaining tungsten oxide is preferably 1.0 wt %:0.5 wt %:98.5 wt%=tungsten oxide:zinc oxide:indium oxide. The composition ratio ofindium oxide containing titanium oxide is preferably 1.0 to 5.0 wt%:99.0 to 95.0 wt %=titanium oxide:indium oxide. The composition ratioof indium tin oxide (ITO) is preferably 10.0 wt %:90.0 wt %=tinoxide:indium oxide. The composition ratio of indium zinc oxide (IZO) ispreferably 10.7 wt %:89.3 wt %=zinc oxide:indium oxide. The compositionratio of indium tin oxide containing titanium oxide is preferably 5.0 wt%:10.0 wt %:85.0 wt %=titanium oxide:tin oxide:indium oxide. Theaforementioned composition ratios are just examples and the compositionratio may be set appropriately.

Further, when a material such as a metal film having no lighttransmissivity is formed thin (preferably a thickness of about 5 to 30nm) so as to be able to transmit light, light can be emitted from thefirst electrode 185. As a metal thin film which can be used for thefirst electrode layer 185, a conductive film formed of titanium,tungsten, nickel, gold, platinum, silver, aluminum, magnesium, calcium,lithium, or an alloy thereof, or the like can be used.

The first electrode layer 185 can be formed by a vapor depositionmethod, a sputtering method, a CVD method, a printing method, a dropletdischarge method, or the like. In this embodiment mode, the firstelectrode layer 185 is formed of indium zinc oxide containing tungstenoxide by a sputtering method. The first electrode layer 185 ispreferably formed with a total thickness of 100 to 800 nm, and is formedwith a thickness of 125 nm in this embodiment mode.

The first electrode layer 185 may be cleaned by a polyvinylalcohol-based porous body or polished by a CMP method so as to planarizethe surface. Moreover, after polishing the first electrode layer by aCMP method, ultraviolet ray irradiation or oxygen plasma treatment maybe applied to the surface of the first electrode layer 185.

After forming the first electrode layer 185, thermal treatment may beperformed. By this thermal treatment, moisture contained in the firstelectrode layer 185 is discharged. Therefore, as the first electrodelayer 185 does not generate degasification or the like, even when alight emitting material which easily deteriorates due to moisture isformed over the first electrode layer 185, the light emitting materialdoes not deteriorate. As a result, a highly reliable display device canbe manufactured.

Next, an insulating layer 186 (called a partition, a barrier, or thelike) is formed to cover an edge portion of the first electrode layer185 and the source electrode layer or the drain electrode layer (seeFIG. 9B). Moreover, in the same step, insulating layers 187 a and 187 bare formed in the external terminal connecting region 202.

When the selection ratio between the first electrode layer 185 and theinsulating layer 186 is high, the first electrode layer 185 functions asan etching stopper when forming the insulating layer 186 functioning asa partition covering a portion of the first electrode layer 185 byetching into a desired shape.

The insulating layer 186 can be formed of silicon oxide, siliconnitride, silicon oxynitride, aluminum oxide, aluminum nitride, aluminumoxynitride, other inorganic insulating materials, acrylic acid,methacrylic acid, a derivative of these, heat resistant high molecularmaterial such as polyimide, aromatic polyamide, or polybenzimidazole, orsiloxane resin. The insulating layer 186 may be formed of aphotosensitive or non-photosensitive material such as acrylic andpolyimide. Moreover, oxazole resin can also be used, which is, forexample, photosensitive polybenzoxazole. Photosensitive polybenzoxazolehas a low dielectric constant (a dielectric constant of 2.9 at a normaltemperature at 1 MHz), high heat resistance (TGA: Thermal GravityAnalysis) thermal decomposition temperature of 550° C. with the rise intemperature at 5° C./min), and a low moisture absorbing rate (0.3% in 24hours at a normal temperature). The insulating layer 186 preferably hasa shape with a continuously changing curvature radius, thereby anelectroluminescent layer 188 and a second electrode layer 189 can haveimproved coverage.

In the connecting region 205 shown in FIG. 10A, a wiring layer formed ofthe same material and in the same step as the second electrode layer iselectrically connected to a wiring layer formed of the same material andin the same step as the gate electrode layer. For this connection, anopening to expose the wiring layer formed of the same material in thesame step as the gate electrode layer is formed. By covering a step inthe periphery of the opening with the insulating layer 186 so as tosmooth the step, the coverage of the second electrode layer 189 can beimproved.

Further, in order to further improve the reliability, it is preferableto perform degasification by vacuum heating before forming theelectroluminescent layer 188. For example, before performing evaporationof an organic compound material, it is preferable to perform thermaltreatment in a reduced pressure atmosphere or an inert gas atmosphere at200 to 400° C., or preferably 250 to 350° C. in order to remove gascontained in the substrate. Moreover, it is preferable to form theelectroluminescent layer 188 by a vacuum vapor deposition method or adroplet discharge method at a reduced pressure without exposing theelectroluminescent layer 188 to air. By this thermal treatment, moisturecontained and attached to the conductive layer as the first electrodelayer and the insulating layer (partition) can be discharged. Thisthermal treatment may include the prior heating step if the substratecan be carried through the vacuum chambers without breaking the vacuum,in which case the prior heating step may be performed once after theinsulating layer (partition) is formed. Here, when the interlayerinsulating film and the insulating layer (partition) are formed of ahighly heat resistant substance, the thermal treatment step can besufficiently performed to improve the reliability.

The electroluminescent layer 188 is formed over the first electrodelayer 185. It is to be noted that only one pixel is shown in FIG. 10B,however, electric field electrode layers corresponding to each of red(R), green (G), and blue (B) are separately formed in this embodimentmode.

A material (a low or high molecular material or the like) which exhibitslight emission of red (R), green (G), or blue (B) can also be formed bya droplet discharge method.

Next, a second electrode layer 189 formed of a conductive film isprovided over the electroluminescent layer 188. As the second electrodelayer 189, a material having a low work function (Al, Ag, Li, Ca, Mg,In, or an alloy or a compound thereof such as MgAg, MgIn, AlLi, CaF₂, orcalcium nitride) may be used. In this manner, a light emitting element190 formed of the first electrode layer 185, the electroluminescentlayer 188, and the second electrode layer 189 is formed (see FIG. 10B).

In the display device of this embodiment mode shown in FIGS. 10A and10B, the light emitted from the light emitting element 190 is emittedfrom the first electrode layer 185 side and passes through in adirection of an arrow shown in FIG. 10B.

In this embodiment mode, an insulating layer may be provided as apassivation film (protective film) over the second electrode layer 189.It is effective to provide a passivation film so as to cover the secondelectrode layer 189 in this manner. As the passivation film, aninsulating film containing silicon nitride, silicon oxide, siliconoxynitride (SiON), silicon nitride oxide (SiNO), aluminum nitride (AlN),aluminum oxynitride (AlON), aluminum nitride oxide containing nitrogenmore than oxygen (AlNO), aluminum oxide, diamond-like carbon (DLC), or anitrogen-containing carbon film (CN) can be used as a single layer or incombination as stacked layers. Alternatively, siloxane resin can also beused.

At this time, it is preferable to use a film having favorable coverageas a passivation film, such as a carbon film. In particular, a DLC filmis effectively used. A DLC film can be formed at a temperature range ofa room temperature to 100° C.; therefore, it can be easily formed overthe electroluminescent layer 188 with low heat resistance as well. TheDLC film can be formed by a plasma CVD method (typically an RF plasmaCVD method, a microwave CVD method, an electron cyclotron resonant (ECR)CVD method, a thermal filament CVD method, or the like), a combustionmethod, a sputtering method, an ion beam vapor deposition method, alaser vapor deposition method, or the like. A reaction gas used forforming the DLC film is a hydrogen gas and a hydrocarbon-based gas (forexample, CH₄, C₂H₂, C₆H₆, or the like), which are ionized by glowdischarging, and thus generated ions are accelerated to collide with anegatively self-biased cathode, thereby the DLC film is formed.Moreover, the CN film is preferably formed by using a C₂H₄ gas and a N₂gas as reaction gases. The DLC film has a high blocking effect againstoxygen and can suppress the oxidization of the electroluminescent layer188. Therefore, a problem can be prevented in that theelectroluminescent layer 188 is oxidized during a subsequent sealingstep.

In this manner, the substrate 100 over which the light emitting element190 is formed and a sealing substrate 195 are fixed to each other by asealing material 192, thereby the light emitting element is sealed (seeFIGS. 10A and 10B). In the display device of the invention, the sealingmaterial 192 and the insulating layer 186 are formed apart from eachother so as not to have a contact. When the sealing material and theinsulating layer 186 are formed apart from each other in this manner,moisture does not easily enter even when using an insulating materialformed of an organic material having a high moisture absorbing propertyfor the insulating layer 186. Thus, deterioration of a light emittingelement can be prevented and reliability of a display device isimproved. As the sealing material 192, it is preferable to use visiblelight curable, ultraviolet curable, or heat curable resinrepresentatively. For example, epoxy resin such as bisphenol A typeliquid resin, bisphenol A type solid resin, bromine epoxy resin,bisphenol F type resin, bisphenol AD type resin, phenol resin, cresolresin, novolac resin, cyclic aliphatic epoxy resin, epi-bis epoxy resin,glycidyl ester based resin, glycidyl amine based resin, heterocyclicepoxy resin, or modified epoxy resin can be used. It is to be noted thata region surrounded by the sealing material may be filled with a fillingmaterial 193. Alternatively, the filling material 193 may fill a regionwith nitrogen or the like by sealing the substrates in a nitrogenatmosphere. As a bottom emission type is employed in this embodimentmode, the filling material 193 is not required to have lighttransmissivity. However, in the case of extracting light through thefilling material 193, the filling material 193 is required to have lighttransmissivity. Typically, visible light, ultraviolet ray, or heatcurable epoxy resin is preferably used. By the aforementioned steps, adisplay device having a display function using a light emitting elementin this embodiment mode is completed. The filling material can bedropped in a liquid state so as to be filled in the display device.

A drop filling method using a dispenser method is described withreference to FIG. 24. The drop filling method shown in FIG. 24 includesa controlling apparatus 40, an image pick-up unit 42, a head 43, afilling material 33, a marker 35, a marker 45, a barrier layer 34, asealing material 32, a TFT substrate 30, and a counter substrate 20. Aclosed loop is formed by the sealing material 32, and then the fillingmaterial 33 is dropped therein from the head 43 once or a plurality oftimes. The filling material having high viscosity is continuouslydischarged and attached to a forming region without being cut off. Onthe other hand, the filling material having low viscosity isintermittently discharged and dropped as shown in FIG. 24. At that time,in order to prevent reaction of the sealing material 32 and the fillingmaterial 33, the barrier layer 34 may be provided. Subsequently, thesubstrates are attached in vacuum and cured by ultraviolet ray; therebyfilled with the filling material. By using a substance having a moistureabsorbing property such as a drying agent as the filling material, afurther moisture absorbing effect is obtained and deterioration ofelements can be prevented.

In order to prevent deterioration of elements due to moisture, a dryingagent is provided in the EL display panel. In this embodiment mode, thedrying agent is provided in a depression portion formed in the sealingsubstrate so as to surround the pixel region, therefore, it does notdisturb thin design. Further, as a large moisture absorbing area isprovided by forming a drying agent in a region corresponding to the gatewiring layer, a high moisture absorbing effect can be obtained. Inaddition, when a drying agent is formed over the gate wiring layer whichdoes not directly emit light, reduction in light extracting efficiencycan be prevented.

It is to be noted in this embodiment mode that the light emittingelement is sealed by a glass substrate; however, as the light emittingelement is sealed in order to protect it from moisture, a method tomechanically seal with a cover material, a method to seal with heatcurable resin or ultraviolet curable resin, a method to seal with a thinfilm having a high barrier property such as metal oxide, nitride, or thelike can also be used. As the cover material, glass, ceramics, plastic,or metal can be used, which is required to have light transmissivitywhen light is emitted to the cover material side. The cover material andthe substrate over which the aforementioned light emitting element isformed are attached to each other by using a sealing material such asheat curable resin or ultraviolet curable resin. Then, the resin iscured by thermal treatment or ultraviolet ray irradiation treatment toform an enclosed space. It is also effective to provide a moistureabsorbing material typified by barium oxide in the enclosed space. Themoisture absorbing material may be provided on a sealing material, overor in the periphery of the partition which does not disturb light fromthe light emitting element. Further, it is possible to fill the spacebetween the cover material and the substrate over which the lightemitting element is formed with heat curable resin or ultravioletcurable resin. In this case, it is effective to add a moisture absorbingmaterial typified by barium oxide in the heat curable resin orultraviolet curable resin.

FIG. 14 shows an example to connect the source electrode layer or drainelectrode layer 172 b to the first electrode layer through a wiringlayer so as to be electrically connected instead of directly connected.In the display device shown in FIG. 14, the source electrode layer ordrain electrode layer of the thin film transistor which drives the lightemitting element and a first electrode layer 790 are electricallyconnected through a wiring layer 199. Moreover, in FIG. 14, the firstelectrode layer 790 is partially stacked over the wiring layer 199;however, the first electrode layer 790 may be formed first and then thewiring layer 199 may be formed on the first electrode layer 790.

In this embodiment mode, an FPC 194 is connected to the terminalelectrode layer 178 by an anisotropic conductive layer 196 at theexternal terminal connecting region 202 so as to have an electricalconnection with outside. Moreover, as shown in FIG. 10A which is a topplan view of the display device, the display device manufactured in thisembodiment mode includes a peripheral driver circuit region 207 and aperipheral driver circuit region 208 having a scan line driver circuitin addition to the peripheral driver circuit region 204, and aperipheral driver circuit region 209 having a signal line drivercircuit.

In this embodiment mode, the aforementioned circuits are used; however,the invention is not limited to this and an IC chip may be mounted as aperipheral driver circuit by a COG method or a TAB method. Moreover, agate line driver circuit and a source line driver circuit may beprovided in any number.

Moreover, a driving method to display an image is not particularlylimited in a display device of the invention. For example, a dotsequential driving method, a line sequential driving method, an areasequential driving method, or the like is preferably used.Representatively, a line sequential driving method is used incombination with a time division grayscale driving method or an areagrayscale driving method appropriately. Further, a video signal inputtedto the source line of the display device may be an analog signal or adigital signal. A driver circuit or the like is to be designedappropriately in accordance with the video signal.

Furthermore, in a display device using a digital video signal, a videosignal inputted to a pixel includes a video signal at a constant voltage(CV) and a video signal at a constant current (CC). The video signal ata constant voltage (CV) is further classified into a video signal with aconstant voltage applied to a light-emitting element (CVCV), and a videosignal with a constant current applied to a light-emitting element(CVCC). In addition, the video signal at a constant current (CC) isclassified into a video signal with a constant voltage applied to alight-emitting element (CCCV), and a video signal with a constantcurrent applied to a light-emitting element (CCCC).

This embodiment mode can be implemented in combination with each ofEmbodiment Modes 1 to 4.

By using the invention, a highly reliable semiconductor device can bemanufactured through simplified steps. Therefore, a semiconductor deviceand a display device with high resolution and high image quality can bemanufactured at low cost and high yield.

Embodiment Mode 6

An embodiment mode of the invention is described with reference to FIGS.11A to 13. This embodiment mode shows an example where the secondinterlayer insulating layer (the insulating layers 181 and 182) is notformed in the display device manufactured in Embodiment Mode 5.Therefore, description on the same portion or a portion having a similarfunction is not repeated.

As described in Embodiment Mode 5, the thin film transistors 173, 174,175, and 176, and the insulating films 167 and 168 are formed over thesubstrate 100. Each thin film transistor has a source electrode layerand a drain electrode layer connected to the source region or the drainregion of the semiconductor layer. A first electrode layer 770 is formedin contact with the source electrode layer or drain electrode layer 172b in the thin film transistor 176 provided in the pixel region 206 (seeFIGS. 11A and 11B).

The first electrode layer 770 which functions as a pixel electrode maybe formed of a similar material and in a similar step to the firstelectrode layer 185 in Embodiment Mode 5. In this embodiment mode also,a light transmissive material is used to extract light through the firstelectrode layer 770 similarly to Embodiment Mode 1. In this embodimentmode, ITSO as a transparent conductive film is used for the firstelectrode layer 770 and etched into a desired shape.

The insulating layer 186 is formed so as to cover an edge portion of thefirst electrode layer 770 and the thin film transistors. In thisembodiment mode, a coated film using a siloxane material (inorganicsiloxane or organic siloxane) is used to form the insulating layer 186.

The electroluminescent layer 188 is formed over the first electrodelayer and the second electrode layer 189 is stacked thereover; therebythe light emitting element 190 is formed. The FPC 194 is adhered to theterminal electrode layer 178 through the anisotropic conductive layer196 in the external terminal connecting region 202. The substrate 100 isattached to the sealing substrate 195 by the sealing material 192 andthe display device is filled with the filling material 193 (see FIG.12). In the display device of this embodiment mode, the sealing material192 and the insulating layer 186 are formed apart from each other so asnot to have a contact. When the sealing material and the insulatinglayer 186 are formed apart from each other in this manner, moisture doesnot easily enter even when using an insulating material using an organicmaterial having a high moisture absorbing property for the insulatinglayer 186. Thus, deterioration of a light emitting element can beprevented and reliability of a display device is improved.

The display device shown in FIG. 13 is an example where a firstelectrode layer 780 corresponding to the first electrode layer 770 isselectively formed over the insulating film 168 before forming a sourceelectrode layer or drain electrode layer 781 corresponding to the sourceelectrode layer or drain electrode layer 172 b connected to the thinfilm transistor 176. In this case, the source electrode layer or drainelectrode layer 781 is stacked over the first electrode layer 780 inthis embodiment mode. When the first electrode layer 780 is formed priorto the source electrode layer or drain electrode layer 781, the sourceelectrode layer or drain electrode layer 781 can be formed over a planeforming region. Therefore, there is an advantage in that favorablecoverage can be obtained and polishing treatment such as CMP can besufficiently performed, and thus the source electrode layer or drainelectrode layer 781 can be formed with good planarity.

A display device shown in FIG. 33 is an example where an insulating film771 covering the source electrode layer or drain electrode layer 172 band the insulating film 168 is formed after forming the source electrodelayer or drain electrode layer 172 b. The insulating film 771 functionsas a passivation film and also as a planarizing film. The insulatingfilm 771 can be formed of a similar material by a similar method to theinsulating film 168. In FIG. 33, a silicon oxynitride film is formedwith a thickness of 50 to 500 nm, preferably 100 to 300 nm (in thisembodiment mode, 100 nm) by a plasma CVD method. An opening to reach thesource electrode layer or drain electrode layer 172 b is formed in theinsulating film 771 and an opening to reach the terminal electrode layer178 is formed in the external terminal connecting region 202. The firstelectrode layer 772 is formed so as to cover the opening, and the sourceelectrode layer or drain electrode layer 172 b and the first electrodelayer 772 are electrically connected.

By the invention, a highly reliable semiconductor device can bemanufactured through simplified steps. Therefore, a semiconductor devicewith high resolution and high image quality can be manufactured at lowcost and high yield.

Embodiment Mode 7

A display device having a light emitting element can be formed by theinvention. The light from the light emitting element is emitted tobottom, top, or dual surfaces. In this embodiment mode, a dual emissiontype and a top emission type are described with reference to FIGS. 15and 16.

A display device shown in FIG. 16 includes an element substrate 1300,thin film transistors 1355, 1365, 1375, and 1385, wiring layers 1324 aand 1324 b, a first electrode layer 1317, an electroluminescent layer1319, a second electrode layer 1320, a filling material 1322, a sealingmaterial 1325, insulating layers 1301 and 1301 b, a gate insulatinglayer 1310, insulating films 1311 and 1312, an insulating layer 1314, asealing substrate 1323, wiring layers 1345 a and 1345 b, terminalelectrode layers 1381 a and 1381 b, an anisotropic conductive layer 1382and an FPC 1383. The display device includes an external terminalconnecting region 222, a wiring region 223, a peripheral driver circuitregion 224, and a pixel region 226. The filling material 1322 can beformed by dropping a liquid composition as in a dropping method of FIG.24. The element substrate 1300 over which the filling material is formedby the dropping method and the sealing substrate 1323 are attached toseal a light emitting display device.

A wiring layer (functions as a source electrode layer or a drainelectrode layer) connected to each of the thin film transistors 1355,1365, 1375, and 1385 has a two-layer structure. The wiring layer 1324 aand the wiring layer 1324 b are also stacked. The wiring layer 1324 bextends to exist outside an edge portion of the wiring layer 1324 a. Thewiring layer 1324 b and the first electrode layer 1317 are formed tocontact each other. Moreover, in the wiring region 223, edge portions ofthe gate insulating layer 1310, the insulating film 1311, and theinsulating film 1312 are etched into tapered shapes of which edgeportions are covered with the wiring layers 1345 a and 1345 b. In thismanner, by using a mask layer formed of an exposure mask provided with adiffraction grating pattern or an auxiliary pattern formed of asemi-transmissive film having a light intensity reducing function, whichenables to form a resist mask layer accurately, different shapes can befreely formed by etching even in the same step.

The display device shown in FIG. 16 is a dual emission type which emitslight in directions of arrows to the element substrate 1300 side and thesealing substrate 1323 side as well. Therefore, light transmissiveelectrode layers are used for the first electrode layer 1317 and thesecond electrode layer 1320.

In this embodiment mode, the first electrode layer 1317 and the secondelectrode layer 1320 are preferably formed of light transmissiveconductive films formed of a conductive material having lighttransmissivity in specific, such as indium oxide containing tungstenoxide, indium zinc oxide containing tungsten oxide, indium oxidecontaining titanium oxide, and indium tin oxide containing titaniumoxide. It is needless to say that indium tin oxide (ITO), indium zincoxide (IZO), indium tin oxide to which silicon oxide is added (ITSO),and the like can also be used.

An example of a composition ratio in each light transmissive conductivematerial is described. In indium oxide containing tungsten oxide, thecomposition ratio may be 1.0 wt %:99.0 wt %=tungsten oxide:indium oxide.In indium zinc oxide containing tungsten oxide, 1.0 wt %:0.5 wt %:98.5wt %=tungsten oxide:zinc oxide:indium oxide. In indium oxide containingtitanium oxide, 1.0 to 5.0 wt %:99.0 to 95.0 wt %=titanium oxide:indiumoxide. In indium tin oxide (ITO), 10.0 wt %:90.0 wt %=tin oxide:indiumoxide. In indium zinc oxide (IZO), 10.7 wt %:89.3 wt %=zinc oxide:indiumoxide. Further, in indium tin oxide containing titanium oxide, 5.0 wt%:10.0 wt %:85.0 wt %=titanium oxide:tin oxide:indium oxide. Thecomposition ratios as described above are just examples, and acomposition ratio may be set appropriately.

In addition, even in a case of a non-light-transmissive material such asa metal film is used, when the thickness is made thin (preferably, about5 to 30 nm) so as to be able to transmit light, light can be emittedfrom the first electrode layer 1317 and the second electrode layer 1320.As a metal thin film that can be used for the first electrode layer 1317and the second electrode layer 1320, a conductive film formed oftitanium, tungsten, nickel, gold, platinum, silver, aluminum, magnesium,calcium, lithium, or an alloy thereof can be given.

As described above, in the display device shown in FIG. 16, lightemitted from the light emitting element 1305 passes through both thefirst electrode layer 1317 and the second electrode layer 1320 and isemitted from both surfaces.

In the display device shown in FIG. 16, the wiring layer 1324 a as asource electrode layer or a drain electrode layer of the thin filmtransistor 1355 and the first electrode layer 1317 of the light emittingelement as a pixel electrode layer are not directly stacked to beelectrically connected. Instead, the wiring layer 1324 a and the firstelectrode layer 1317 are electrically connected to each other throughthe wiring layer 1324 b formed under the wiring layer 1324 a. With sucha structure, even when the wiring layer 1324 a and the first electrodelayer 1317 are formed of materials which are not easily electricallyconnected by direct connection or materials which generate deteriorationsuch as electric corrosion when contacted to each other, such materialscan be used since the wiring layer 1324 b is interposed therebetween. Asa result, choice of materials which can be used for the wiring layer1324 a and the first electrode layer 1317 expands. As a problem causedby stacking the wiring layer 1324 a and the first electrode layer 1317is not required to be considered, a material having characteristicsrequired for each of the wiring layer 1324 a or the drain electrodelayer and the first electrode layer 1317 can be freely selected.Therefore, a display device with high functionality and higherreliability can be manufactured at high yield. A connection between thesource electrode layer or drain electrode layer and the first electrodelayer is similar to a display device shown in FIG. 15.

The display device shown in FIG. 15 has a top emission structure inwhich light is emitted in a direction of an arrow. The display deviceshown in FIG. 15 includes an element substrate 1600, a thin filmtransistor 1655, a thin film transistor 1665, a thin film transistor1675, a thin film transistor 1685, a wiring layer 1624 a, a wiring layer1624 b, a first electrode layer 1617, an electroluminescent layer 1619,a second electrode layer 1620, a protective film 1621, a fillingmaterial 1622, a sealing material 1625, an insulating film 1601 a, aninsulating film 1601 b, a gate insulating layer 1610, an insulating film1611, an insulating film 1612, an insulating layer 1614, a sealingsubstrate 1623, a wiring layer 1633 a, a wiring layer 1633 b, a terminalelectrode layer 1681 a, a terminal electrode layer 1681 b, ananisotropic conductive layer 1682, and an FPC 1683.

In the display device shown in FIG. 15, an insulating layer stacked overthe terminal electrode layer 1681 is removed by etching. As shown inFIGS. 15 and 16, reliability is further improved with a structure wherean insulating layer having a moisture permeable property is not providedin the periphery of the terminal electrode layer. Moreover, the displaydevice includes an external terminal connecting region 232, a wiringregion 233, a peripheral driver circuit region 234, and a pixel region236. In the wiring region 233, edge portions of the gate insulatinglayer 1610, the insulating film 1611, and the insulating film 1612 areetched into tapered shapes, which are covered with wiring layers 1633 aand 1633 b. In this manner, by using a mask layer formed of an exposuremask provided with a diffraction grating pattern or an auxiliary patternformed of a semi-transmissive film having a light intensity reducingfunction, which enables to form a resist mask layer accurately,different shapes can be freely formed by etching even in the same step.

In the case of the display device shown in FIG. 15, the wiring layer1624 b as a metal layer having reflectivity is formed under the firstelectrode layer 1317 in the dual emission type display device shown inFIG. 16. The first electrode layer 1617 as a transparent conductive filmis formed over the wiring layer 1624 b. As the wiring layer 1624 b whichis required to have reflectivity, a conductive film formed of titanium,tungsten, nickel, gold, platinum, silver, copper, tantalum, molybdenum,aluminum, magnesium, calcium, lithium, an alloy thereof may be used. Itis preferable to use a highly reflective substance in a visible lightregion. In this embodiment mode, a TiN film is used.

For the first electrode layer 1617 and the second electrode layer 1620,in specific, a transparent conductive film formed of a conductivematerial having light transmissivity is preferably used, such as indiumoxide containing tungsten oxide, indium zinc oxide containing tungstenoxide, indium oxide containing titanium oxide, and indium tin oxidecontaining titanium oxide. It is needless to say that indium tin oxide(ITO), indium zinc oxide (IZO), indium tin oxide to which silicon oxideis added (ITSO), and the like can also be used.

Further, when even a material such as a metal film having no lighttransmissivity is formed thin (preferably a thickness of 5 to 30 nm) soas to be able to transmit light, light can be emitted from the secondelectrode layer 1620. As a metal thin film which can be used for thesecond electrode layer 1620, a conductive film formed of titanium,tungsten, nickel, gold, platinum, silver, aluminum, magnesium, calcium,lithium, or an alloy thereof, or the like can be used.

A structure of the light emitting element 190 applicable to thisembodiment mode is described in details with reference to FIGS. 18A to18D.

Each of FIGS. 18A to 18D shows a structure of a light emitting element.A light emitting element includes an electroluminescent layer 860 formedof a mixture of an organic compound and an inorganic compound sandwichedbetween a first electrode layer 870 and a second electrode layer 850.The electroluminescent layer 860 is formed of a first layer 804, asecond layer 803, and a third layer 802 as shown. In particular, thefirst layer 804 and the third layer 802 have notable characteristics.

The first layer 804 functions to transport holes into the second layer803 and includes at least a first organic compound and a first inorganiccompound having an electron acceptor property for the first organiccompound. What is important is not simply that the first organiccompound and the first inorganic compound are mixed, but that the firstinorganic compound has a higher electron acceptor property for the firstorganic compound. With such a structure, a lot of hole carriers aregenerated in the first organic compound which originally has hardly anyinternal carriers, thereby an excellent hole injecting property and holetransporting property can be provided.

Therefore, the first layer 804 can have superior conductivity (a holeinjecting and transporting property particularly in the first layer 804)as well as an effect which is thought to be obtained by mixing aninorganic compound (such as improvement in heat resistance). This effectcannot be obtained in a conventional hole transporting layer in which anorganic compound and an inorganic compound which do not mutually affecteach other electronically are simply mixed. Because of this effect, adriving voltage can be set lower than before. Further, as the firstlayer 804 can be fowled thick without increasing the driving voltage, ashort-circuit of the element caused by dust or the like can also besuppressed.

As described above, hole carriers are generated in the first organiccompound, therefore, it is preferable that the first organic compoundhave a hole transporting property. As the organic compound having a holetransporting property, for example, phthalocyanine (abbreviation: H₂Pc),copper phthalocyanine (abbreviation: CuPc), vanadyl phthalocyanine(abbreviation: VOPc), 4,4′,4″-tris(N,N-diphenylamino)-triphenylamine(abbreviation: TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]-triphenylamine(abbreviation: MTDATA), 1,3,5-tris[N,N-di(m-tolyl)amino]benzene(abbreviation: m-MTDAB),N,N′-diphenyl-N,N-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine(abbreviation: TPD), 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl(abbreviation: NPB),4,4′-bis{N-[4-di(m-tolyl)amino]phenyl-N-phenylamino}biphenyl(abbreviation: DNTPD), and 4,4′,4″-tris(N-carbazolyl)triphenylamine(abbreviation: TCTA). However, the organic compound having a holetransporting property is not limited to these. In addition, of thecompounds mentioned above, aromatic amine compounds as typified byTDATA, MTDATA, m-MTDAB, TPD, NPB, DNTPD, and TCTA easily generate holecarriers, and are a suitable group of compounds for the first organiccompound.

On the other hand, the first inorganic compound may be any material aslong as the material easily accepts electrons from the first organiccompound, and various metal oxides and metal nitrides can be used.However, transition metal oxides each having a transition metal thatbelongs to any one of Groups 4 to 12 of the periodic table are preferredsince an electron accepting property is easily provided. Specifically,the transition metal oxides include titanium oxide, zirconium oxide,vanadium oxide, molybdenum oxide, tungsten oxide, rhenium oxide,ruthenium oxide, and zinc oxide. In addition, of the metal oxidesmentioned above, many of transition metal oxides each having atransition metal that belongs to any one of Groups 4 to 8 have a higherelectron accepting property, which are a preferable group of compounds.In particular, vanadium oxide, molybdenum oxide, tungsten oxide, andrhenium oxide are preferred since these oxides can be used easily forvacuum deposition.

It is to be noted that the first layer 804 may be formed by stacking aplurality of layers each including a combination of an organic compoundand an inorganic compound as described above, or may further includeanother organic or inorganic compound.

Next, the third layer 802 will be described. The third layer 802 is alayer that takes on the function of transporting electrons to the secondlayer 803, includes at least a third organic compound and a thirdinorganic compound that exhibits an electron donating property to thethird organic compound. What is important is that the third inorganiccompound is not only mixed with the third organic compound but alsoexhibits an electron donating property to the third organic compound.This structure generates a lot of electron carriers in the third organiccompound, which originally has hardly any internal carriers, to providean excellent electron injecting and transporting property.

Therefore, the third layer 802 provides not only advantages that areconsidered to be obtained by mixing an inorganic compound (for example,improvement in heat resistance) but also excellent conductivity (inparticular, electron injecting and transporting properties in the caseof the third layer 802). This excellent conductivity is an advantagethat is not able to be obtained from a conventional electrontransporting layer in which an organic compound and an inorganiccompound that do not electronically interact with each other are simplymixed. This advantage makes it possible to lower a driving voltage morethan ever before. In addition, since the third layer 802 can be madethicker without causing an increase in driving voltage, a short circuitof an element due to dust and the like can also be suppressed.

Meanwhile, it is preferable to use an electron-transporting organiccompound as the third organic compound since electron carriers aregenerated in the third organic compound as described above. Examples ofthe electron-transporting organic compound include, but are not limitedto, tris(8-quinolinolato)aluminum (abbreviation: Alq₃),tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq₃),bis(10-hydroxybenzo[h]quinolinato)beryllium (abbreviation: BeBq₂),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation:BAlq), bis[2-(2′-hydroxyphenyl)-benzoxazolato]zinc (abbreviation:Zn(BOX)₂) or bis[2-(2′-hydroxyphenyl)benzothiazolato]zinc (abbreviation:Zn(BTZ)₂), bathophenanthroline (abbreviation: BPhen), bathocuproin(abbreviation: BCP),2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis[5-(4-tert-butylphenyl)-1,3,4-oxadiazole-2-yl]benzene(abbreviation: OXD-7),2,2′,2″-(1,3,5-benzenetriyl)-tris(1-phenyl-1H-benzimidazole)(abbreviation: TPBI),3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ), and3-(4-biphenylyl)-4-(4-ethylphenyl)-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: p-EtTAZ). In addition, of the compounds mentioned above,chelate metal complexes each having a chelate ligand including anaromatic ring as typified by Alq₃, Almq₃, BeBq₂, BAlq, Zn(BOX)₂, andZn(BTZ)₂, organic compounds each having a phenanthroline skeleton astypified by BPhen and BCP, and organic compounds each having anoxadiazole skeleton as typified by PBD and OXD-7 easily generateelectron carriers, and are suitable groups of compounds for the thirdorganic compound.

On the other hand, the third inorganic compound may be any material aslong as the material easily donates electrons from the third organiccompound, and various metal oxides and metal nitrides can be used.However, alkali metal oxides, alkaline-earth metal oxides, rare-earthmetal oxides, alkali metal nitrides, alkaline-earth metal nitrides, andrare-earth metal nitrides are preferred since an electron donatingproperty is easily provided. Specifically, examples of the oxidesmentioned above include lithium oxide, strontium oxide, barium oxide,erbium oxide, lithium nitride, magnesium nitride, calcium nitride,yttrium nitride, and lanthanum nitride. In particular, lithium oxide,barium oxide, lithium nitride, magnesium nitride, and calcium nitrideare preferred since these oxides and nitrides can be used easily forvacuum deposition.

It is to be noted that the third layer 802 may be formed by stacking aplurality of layers each including a combination of an organic compoundand an inorganic compound as described above, or may further includeanother organic compound or inorganic compound.

Next, the second layer 803 will be described. The second layer 803 is alayer that takes on the function of emitting light, and includes atleast a second organic compound that is luminescent and may include asecond inorganic compound. The second layer 803 can be formed by mixingsome of various luminescent organic compounds and inorganic compounds.However, since it is considered that a current does not easily flowthrough the second layer 803 as compared with the first layer 804 or thethird layer 802, it is preferable that the thickness of the second layer803 be approximately 10 to 100 nm.

The second organic compound is not particularly limited as long as aluminescent organic compound is used, and examples of the second organiccompound include 9,10-di(2-naphthyl)anthracene (abbreviation: DNA),9,10-di(2-naphthyl)-2-tert-butylanthracene (abbreviation: t-BuDNA),4,4′-bis(2,2-diphenylvinyl)biphenyl (abbreviation: DPVBi), coumarin 30,coumarin 6, coumarin 545, coumarin 545T, perylene, rubrene,periflanthene, 2,5,8,11-tetra(tert-butyl)perylene (abbreviation: TBP),9,10-diphenylanthracene (abbreviation: DPA), 5,12-diphenyltetracene,4-(dicyanomethylene)-2-methyl-[p-(dimethylamino)styryl]-4H-pyran(abbreviation: DCM1),4-(dicyanomethylene)-2-methyl-6-[2-(julolidine-9-yl)ethenyl]-4H-pyran(abbreviation: DCM2), and4-(dicyanomethylene)-2,6-bis[p-(dimethylamino)styryl]-4H-pyran(abbreviation: BisDCM). In addition, it is also possible to usecompounds that are capable of producing phosphorescence such asbis[2-(4′,6′-difluorophenyl)pyridinato-N,C²′]iridium(picolinate)(abbreviation: FIrpic),bis{2-[3′,5′-bis(trifluoromethyl)phenyl]pyridinato-N,C²′}iridium(picolinate)(abbreviation: Ir(CF₃ ppy)₂(pic)), tris(2-phenylpyridinato-N,C²′)iridium(abbreviation: Ir(ppy)₃),bis(2-phenylpyridinato-N,C²′)iridium(acetylacetonate) (abbreviation:Ir(ppy)₂(acac)),bis[2-(2′-thienyl)pyridinato-N,C³′]iridium(acetylacetonate)(abbreviation: Ir(thp)₂(acac)),bis(2-phenylquinolinato-N,C²′)iridium(acetylacetonate) (abbreviation:Ir(pq)₂(acac)), andbis[2-(2′-benzothienyl)pyridinato-N,C³′]iridium(acetylacetonate)(abbreviation: Ir(btp)₂(acac)).

Moreover, the second layer 803 may be formed of not only asinglet-excited light-emitting material but also a triplet-excitedlight-emitting material including a metal complex or the like. Forexample, among pixels for emitting red, green, and blue light, the pixelfor emitting the red color, which has a relatively short half brightnesslife period of luminance, is formed of the triplet-excitedlight-emitting material and the other two pixels are formed of thesinglet-excited light-emitting material. The triplet-excitedlight-emitting material has an advantage of low power consumption toobtain the same luminance as that of the singlet-excited light-emittingmaterial because the triplet-excited light-emitting material has higherlight-emission efficiency. In other words, when the pixel for the redcolor is formed of the triplet-excited light-emitting material, thereliability can be improved because the light-emitting element requiresa smaller amount of current. For lower power consumption, the pixels forthe red and green colors may be formed of the triplet-excitedlight-emitting material and the pixel for the blue color may be formedof the singlet-excited light-emitting material. When the light-emittingelement of the green color that is highly visible to human eyes isformed of the triplet-excited light-emitting material, the powerconsumption can be further reduced.

Further, not only the second layer 803 may include the second organiccompound described above, which produces luminescence, but also anotherorganic compound may be added thereto. Examples of organic compoundsthat can be added include, but are not limited to, TDATA, MTDATA,m-MTDAB, TPD, NPB, DNTPD, TCTA, Alq₃, Almq₃, BeBq₂, BAlq, Zn(BOX)₂,Zn(BTZ)₂, BPhen, BCP, PBD, OXD-7, TPBI, TAZ, p-EtTAZ, DNA, t-BuDNA, andDPVBi, which are mentioned above, and further,4,4′-bis(N-carbazolyl)biphenyl (abbreviation: CBP) and1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB). It is tobe noted that it is preferable that the organic compound, which is addedin addition to the second organic compound as described above, havelarger excitation energy than the second organic compound and be addedmore than the second organic compound in order to make the secondorganic compound produce luminescence efficiently (which makes itpossible to prevent concentration quenching of the second organiccompound). In addition, as another function, the added organic compoundmay produce luminescence along with the second organic compound (whichmakes it possible to produce white luminescence).

The second layer 803 may have a structure for performing color displayby providing each pixel with a light emitting layer having differentemission wavelength bands. Typically, a light emitting layercorresponding to each color of R (red), G (green), and B (blue) isformed. In this case, color purity can be increased and a pixel portioncan be prevented from having a mirror surface (glare) by providing alight emitting side of a pixel with a filter which transmits light of anemission wavelength band. Providing a filter can omit a circularlypolarizing plate or the like which is conventionally used to prevent apixel portion from having a mirror surface (glare) and can eliminate theloss of light emitted from the light emitting layer. Further, a changein tone, which occurs when a pixel portion (display screen) is obliquelyseen, can be reduced.

A high molecular organic light emitting material or a low molecularorganic light emitting material can be used for the material of thesecond layer 803. A high molecular organic light emitting material isphysically stronger than a low molecular material and is superior indurability of the element. In addition, a high molecular organic lightemitting material can be formed by coating; therefore, the element canbe manufactured relatively easily.

The emission color is determined depending on a material forming thelight emitting layer; therefore, a light emitting element which displaysdesired luminescence can be formed by selecting an appropriate materialfor the light emitting layer. As a high molecular electroluminescentmaterial which can be used for forming a light emitting layer, apolyparaphenylene-vinylene-based material, a polyparaphenylene-basedmaterial, a polythiophene-based material, or a polyfluorene-basedmaterial can be used.

As the polyparaphenylene vinylene-based material, a derivative ofpoly(paraphenylenevinylene) [PPV], for example,poly(2,5-dialkoxy-1,4-phenylenevinylene) [RO-PPV];poly(2-(2′-ethyl-hexoxy)-5-methoxy-1,4-phenylenevinylene) [MEH-PPV];poly(2-(dialkoxyphenyl)-1,4-phenylenevinylene) [ROPh-PPV]; and the likecan be used. As the polyparaphenylene-based material, a derivative ofpolyparaphenylene [PPP], for example, poly(2,5-dialkoxy-1,4-phenylene)[RO-PPP]; poly(2,5-dihexoxy-1,4-phenylene); and the like can be used. Asthe polythiophene-based material, a derivative of polythiophene [PT],for example, poly(3-alkylthiophene) [PAT]; poly(3-hexylthiophen) [PHT];poly(3-cyclohexylthiophen) [PCHT]; poly(3-cyclohexyl-4-methylthiophene)[PCHMT]; poly(3,4-dicyclohexylthiophene) [PDCHT];poly[3-(4-octylphenyl)-thiophene] [POPT];poly[3-(4-octylphenyl)-2,2-bithiophene] [PTOPT]; and the like can beused. As the polyfluorene-based material, a derivative of polyfluorene[PF], for example, poly(9,9-dialkylfluorene) [PDAF];poly(9,9-dioctylfluorene) [PDOF]; and the like can be used.

The second inorganic compound may be any inorganic material as long asluminescence of the second organic compound is not easily subject toquenching by the inorganic compound, and various metal oxides and metalnitrides can be used. In particular, metal oxides each having a metalthat belongs to Group 13 or 14 of the periodic table are preferred sinceluminescence of the second organic compound is not easily subject toquenching, and specifically, aluminum oxide, gallium oxide, siliconoxide, and germanium oxide are preferred. However, the second inorganiccompound is not limited thereto.

It is to be noted that the second layer 803 may be formed by stacking aplurality of layers each including a combination of the organic compoundand the inorganic compound as described above, or may further includeanother organic or inorganic compound. The structure of the lightemitting layer may vary. Such changes as dispersing a light emittingmaterial and providing a dedicated electrode layer instead of providinga specific electron injecting region or light emitting region areconstrued as being included in the invention unless such changes departfrom the scope of the invention.

A light emitting element formed with the above described materials emitslight by being forward biased. A pixel of a display device formed with alight emitting element can be driven by a simple matrix mode or anactive matrix mode. In any event, each pixel emits light by applying aforward bias thereto at a specific timing; however, the pixel is in anon-light-emitting state for a certain period. Reliability of a lightemitting element can be improved by applying a reverse bias in thenon-light-emitting time. In a light emitting element, there is adeterioration mode in which emission intensity is decreased underspecific driving conditions or a deterioration mode in which anon-light-emitting region is enlarged in the pixel and luminance isapparently decreased. However, progression of deterioration can beslowed down by alternating current driving where bias is applied forwardand reversely. Thus, reliability of a light emitting device can beimproved. Additionally, either of digital driving and analog driving canbe applied.

In the case of a top emission type and dual emission type displaydevice, a color filter (colored layer) may be formed over the sealingsubstrate. The color filter (colored layer) can be formed by adeposition method or a droplet discharge method. With the use of thecolor filter (colored layer), high-definition display can also beperformed. This is because a broad peak can be modified by the colorfilter (colored layer) to be sharp in light emission spectrum of eachRGB.

Full color display can be performed by forming a material which exhibitslight emission of a single color and combining a color filter and acolor conversion layer. The color filter (colored layer) or the colorconversion layer may be formed over, for example, a second substrate (asealing substrate) and may be attached to a substrate.

Naturally, display may be performed in monochrome. For example, an areacolor type display device may be manufactured by using single coloremission. The area color type is suitable for a passive matrix typedisplay area, and can mainly display text and symbols.

The materials of the first electrode layer 870 and the second electrodelayer 850 are required to be selected considering the work functions.Each of the first electrode layer 870 and the second electrode layer 850can be either an anode or a cathode depending on the pixel structure. Inthe case where a driving thin film transistor has p-type conductivity,the first electrode layer 870 may preferably serve as an anode and thesecond electrode layer 850 may serve as a cathode as shown in FIG. 18A.In the case where the driving TFT has n-type conductivity, the firstelectrode layer 870 may preferably be used as a cathode and the secondelectrode layer 850 may be used as an anode as shown in FIG. 18B.Materials that can be used for the first electrode layer 870 or thesecond electrode layer 850 will be described. It is preferable to use amaterial that has a higher work function (specifically, a material thathas a work function of 4.5 eV or higher) for one of the first electrodelayer 870 and the second electrode layer 850 which serves as an anode,and a material that has a lower work function (specifically, a materialthat has a work function of 3.5 eV or lower) for the other which servesas a cathode. However, since the first layer 804 and the third layer 802are respectively superior in hole injecting and/or transportingproperty, and electron injecting and/or transporting property, eitherthe first electrode layer 870 or the second electrode layer 850 isscarcely restricted on work function, and various materials can be usedfor the first electrode layer 870 and the second electrode layer 850.

Each of the light-emitting elements shown in FIGS. 18A and 18B has astructure in which light is extracted from the first electrode layer870, and thus, the second electrode layer 850 is not always required tohave a light-transmitting property. The second electrode layer 850 maybe formed of a film mainly including an element selected from Ti, Ni, W,Cr, Pt, Zn, Sn, In, Ta, Al, Cu, Au, Ag, Mg, Ca, Li and Mo, or an alloymaterial or a compound material containing the element as its maincomponent such as TiN, TiSi_(x)N_(y), WSi_(x), WN_(x), WSi_(x)N_(y), andNbN, or a stacked film thereof with a total thickness of 100 to 800 nm.

The second electrode layer 850 can be formed by a vapor depositionmethod, a sputtering method, a CVD method, a printing method, a dropletdischarge method, or the like.

In addition, when the second electrode layer 850 is formed by using alight-transmitting conductive material similarly to the material usedfor the first electrode layer 870, light is also extracted from thesecond electrode layer 850, and a dual emission structure can beobtained, in which light emitted from the light-emitting element isemitted from both of the first electrode layer 870 side and the secondelectrode layer 850 side.

It is to be noted that the light-emitting element according to thepresent invention has variations by changing types of the firstelectrode layer 870 and the second electrode layer 850.

FIG. 18B shows a case where the third layer 802, the second layer 803,and the first layer 804 are provided in this order from the firstelectrode layer 870 side in the electroluminescent layer 860.

As described above, in the light-emitting element according to thepresent invention, the layer interposed between the first electrodelayer 870 and the second electrode layer 850 is formed of theelectroluminescent layer 860 including a layer in which an organiccompound and an inorganic compound are combined. The light-emittingelement is an organic-inorganic composite light-emitting elementprovided with layers (that is, the first layer 804 and the third layer802) that provide functions called a high carrier-injecting property andcarrier-transporting property by mixing an organic compound and aninorganic compound, where the functions are not obtainable from onlyeither one of the organic compound and the inorganic compound. Further,the first layer 804 and the third layer 802 are particularly required tobe layers in which an organic compound and an inorganic compound arecombined when provided on the first electrode layer 870 side, and maycontain only one of an organic compound and an inorganic compound whenprovided on the second electrode layer 850 side.

Further, various methods can be used as a method for forming theelectroluminescent layer 860, which is a layer in which an organiccompound and an inorganic compound are mixed. For example, the methodsinclude a co-vapor deposition method of evaporating both an organiccompound and an inorganic compound by resistance heating. In addition,for co-evaporation, an inorganic compound may be evaporated by anelectron beam (EB) while evaporating an organic compound by resistanceheating. Further, the methods also include a method of sputtering aninorganic compound while evaporating an organic compound by resistanceheating to deposit the both at the same time. In addition, theelectroluminescent layer may also be formed by a wet process.

Similarly, for the first electrode layer 870 and the second electrodelayer 850, evaporation by resistance heating, EB evaporation,sputtering, a wet process, and the like can be used.

In FIG. 18C, an electrode layer having reflectivity is used for thefirst electrode layer 870, and an electrode layer having alight-transmitting property is used for the second electrode layer 850in the structure of FIG. 18A. Light emitted from the electroluminescentlayer is reflected by the first electrode layer 870, transmitted throughthe second electrode layer 850, and is emitted outside. Similarly, inFIG. 18D, an electrode layer having reflectivity is used for the firstelectrode layer 870, and an electrode layer having a light-transmittingproperty is used for the second electrode layer 850 in the structure ofFIG. 18B. Light emitted from the electroluminescent layer is reflectedby the first electrode layer 870, transmitted through the secondelectrode layer 850, and is emitted to outside.

This embodiment mode can be freely implemented in combination with eachof Embodiment Modes 1 to 6.

By the invention, a highly reliable display device can be manufacturedthrough simplified steps. Therefore, a display device with highresolution and high image quality can be manufactured at low cost andhigh yield.

Embodiment Mode 8

An embodiment mode of the invention is described with reference to FIGS.17A and 17B. This embodiment mode shows an example of a liquid crystaldisplay device having a liquid crystal display element using a liquidcrystal material as a display element in the display device manufacturedin Embodiment Mode 5. Therefore, description of the same portion or aportion having a similar function is not repeated.

FIG. 17A is a top plan view of a liquid crystal display device. FIG. 17Bis a cross sectional view along a line C-D in FIG. 17A.

A display device shown in FIGS. 17A and 17B include a substrate 600, athin film transistor 620, a thin film transistor 621, a thin filmtransistor 622, a capacitor 623, a pixel electrode layer 630, anorientation film 631, a liquid crystal layer 632, an orientation film633, a counter electrode layer 634, a color filter 635, a countersubstrate 695, a polarizing plate 636 a, a polarizing plate 636 b, asealing material 692, an insulating film 604 a, an insulating film 604b, a gate insulating layer 611, an insulating film 612, an insulatingfilm 615, an insulating film 616, a terminal electrode layer 678, ananisotropic conductive layer 696, an FPC 694, and a spacer 637. Thedisplay device includes a separating region 601, an external terminalconnecting region 602, a sealing region 603, a driver circuit region 608a, a driver circuit region 608 b, and a pixel region 606.

The pixel electrode layer 630 and the counter electrode layer 634 can beformed of a similar material to the first electrode layer 185 of thelight emitting element in a similar step to Embodiment Mode 5. In thecase of a transmissive liquid crystal display device, a material havinglight transmissivity may be used for the pixel electrode layer 630 andthe counter electrode layer 634. In the case of a light reflectiveliquid crystal display device in which light is extracted from thecounter electrode layer 634 side, a material having light reflectivitymay be used for the pixel electrode layer 630.

The alignment film 631 is formed so as to cover the pixel electrodelayer 630 and the thin film transistors by a printing method or a spincoating method. It is to be noted that the alignment film 631 can beselectively formed by a screen printing method or an offset printingmethod. After that, rubbing treatment is applied. Subsequently, thesealing material 692 is formed in a peripheral region of the pixels by adroplet discharge method.

After that, the counter substrate 695 over which the alignment film 633,the counter electrode layer 634, the color filter 635, and thepolarizing plate 636 b are provided and the element substrate 600including the TFTs are attached to each other with a spacer 637interposed therebetween. By providing the liquid crystal layer 632 inthe space, a liquid crystal display device can be manufactured. As theliquid crystal display device of this embodiment mode is a transmissivetype, the polarizing plate 636 a is formed on a side of the elementsubstrate 600, where the TFTs are not formed. The sealing material maybe mixed with filler, and the counter substrate 695 may be furtherprovided with a shielding film (black matrix) or the like. Note that asa method for forming the liquid crystal layer, a dispenser method (onedrop fill method) may be used as well as a dipping method (pump method)by which liquid crystals are injected by utilizing a capillaryphenomenon after attaching the counter substrate 695 to the substrate600.

The one drop fill method employing the dispenser method may be similarlyperformed to the drop filling method of the filling material shown inFIG. 24 in Embodiment Mode 5. Subsequently, the substrates are attachedto each other in vacuum and ultraviolet curing treatment is appliedafter that so as to be filled with the liquid crystals. Further, asealing material may be provided on the TFT substrate side and liquidcrystals may be dropped therein.

With respect to spacers, particles having several μm in size may bedispersed. However, in this embodiment mode, a resin film is formed overthe entire surface of the substrate, and then the resin film is etchedinto desired shapes to form the spaces. After a material for suchspacers is applied by a spinner, the material is patterned into apredetermined shape through light exposure and development treatments.Also, the material is baked at 150 to 200° C. using a clean oven or thelike to be cured. The shapes of these spacers manufactured above can bevaried depending on the conditions of the light exposure and developmenttreatments. Preferably, when the spacers are formed to have a columnarshape that has a flat top and a flat bottom, the liquid crystal displaydevice can secure mechanical strength when being attached to the countersubstrate. Spacers having a cone shape, a pyramidal shape or the likecan be used, and the shapes of the spacers are not particularly limited.

In order to connect inside of the display device manufactured in theabove process to an external wiring substrate, a connection portion isformed. An insulating layer in the connection portion is removed byashing treatment using oxygen gas under atmospheric pressure or almostatmospheric pressure. The ashing treatment uses oxygen gas together withone or more of hydrogen, CF₄, NF₃, H₂O, and CHF₃. In this process, theashing treatment is performed after sealing the liquid crystal with thecounter substrate so as to prevent damage or breakage due toelectrostatic. In the case of having a less possibility of adverseeffect due to electrostatic, however, the ashing treatment can becarried out at any time.

Subsequently, a terminal electrode layer 678 which is electricallyconnected to the pixel portion and an FPC 694 which is a connectionwiring substrate are provided through an anisotropic conductive layer696. The FPC 694 serves to transmit a signal or an electric potentialfrom outside. According to the above mentioned process, a liquid crystaldisplay device having a display function can be formed.

As shown in FIG. 17A, the pixel region 606, the driver circuit region608 a, and the driver circuit region 608 b which function as scan linedriver circuits are sealed between the element substrate 600 and thecounter substrate 695 by the sealing material 692, and the drivercircuit region 607 which functions as a signal line driver circuitformed of a driver IC is provided over the element substrate 600. Adriver circuit including thin film transistors 620 and 621 is providedin a driving region.

In a peripheral driver circuit in this embodiment mode, a CMOS circuitformed of the thin film transistors 620 and 621 is provided, since thethin film transistor 620 is a p-channel thin film transistor and thethin film transistor 621 is an n-channel transistor.

The capacitor 395 described in Embodiment Mode 4 and the capacitor 623can be formed in a similar manner. In the capacitor 623, a firstconductive layer 652 a can be formed wider than a second conductivelayer 652 b. Therefore, an n-type impurity region 651 can be formedwide. The capacitance formed between an impurity region and a gateelectrode is larger than that formed between a gate electrode and aregion to which impurity elements are not added. Therefore, by formingthe n-type impurity region 651 under the first conductive layer 652 awide, large capacitance can be obtained.

The thin film transistor 622 is a double-gate type n-channel thin filmtransistor having an LDD region in a Loff region. The n-type impurityregion formed in the Loff region has effects to alleviate an electricfield in the vicinity of the drain region to prevent deteriorationcaused by hot carrier injection and to reduce an off current. As aresult, a highly reliable display device with low power consumption canbe manufactured.

Embodiment Mode 9

One aspect of the invention where a protective diode is provided in eachof a scan line input terminal portion and a signal line input terminalportion is described with reference to FIG. 23. In FIG. 23, TFTs 501 and502, a capacitor 504, and a pixel electrode layer 503 are provided in apixel 2702.

A protective diode 561 and a protective diode 562 are provided in thesignal line input terminal portion. These protective diodes are formedin a similar step to the TFT 501 or 502 so that a gate and one of adrain and a source are connected to operate as diodes. FIG. 22 shows anequivalent circuit diagram of a top plan view shown in FIG. 23.

The protective diode 561 is constituted by a gate electrode layer, asemiconductor layer, and a wiring layer. The protective diode 562 has asimilar structure. Common potential lines 554 and 555 connected to theseprotective diodes are formed in the same layer as the gate electrodelayer. Therefore, a contact hole is required to be formed in theinsulating layer so that the common potential lines are electricallyconnected to the wiring layer.

A contact hole may be formed in an insulating layer by forming a masklayer and applying etching process. In this case, when etching processby atmospheric pressure discharge is employed, a discharging process canbe performed locally, therefore, a mask layer is not required to beformed over the entire surface of the substrate.

The signal wiring layer is formed of the same layer as a source or drainwiring layer 505 and has a structure in which the signal wiring layerconnected to the source or drain wiring layer 505 is connected to asource side or a drain side of the TFT 501.

The input terminal portion of the scan line also has a similarstructure. A protective diode 563 includes a gate electrode layer, asemiconductor layer, and a wiring layer. A protective diode 564 has asimilar structure. Common potential lines 556 and 557 connected to thisprotective diode are formed in the same layer as the source and drainelectrode layers. The protective diodes provided in an input stage canbe formed at the same time. Note that the positions to provide theprotective diodes are not limited to this embodiment mode and can bealso provided between a driver circuit and a pixel.

As shown in the top plan view of FIG. 23, the wiring layer has a patternwhere a corner that is a right triangle in each edge bent into an Lshape is removed so that one side of the triangle is 10 μm or shorter,or equal to or longer than one-fifth the line width of the wiring layerand equal to or shorter than half the line width of the wiring layer,thereby the edge is rounded. That is to say, the circumference of thewiring layer in the edge is curved when seen from above. Corners arerounded by removing sharp corners with equal to or longer than one-fifththe width of the wiring layer and equal to or shorter than half thewidth of the wiring layer. Specifically, in order to form a roundcircumference of the edge, a part of the wiring layer is removed, whichcorresponds to an isosceles right triangle having two first straightlines that are perpendicular to each other making the edge, and a secondstraight line that makes an angle of about 45 degrees with the two firststraight lines. When removing the triangle, two obtuse angles are formedin the wiring layer. At this time, the wiring layer is preferably etchedby appropriately adjusting the etching conditions and/or a mask designso that a curved line in contact with the first straight line and thesecond straight line is formed in each obtuse angle part. Note that thelength of the two sides of the isosceles right triangle, which are equalto each other, is equal to or longer than one-fifth of the width of thewiring layer and equal to or shorter than half the width of the wiringlayer. In addition, the inner circumference of the edge is also madecurved in accordance with the circumference of edge.

When the wiring layer is thus disposed so that the corner and theportion where the wire width changes are curved, generation of fineparticles due to abnormal discharge can be suppressed in dry etchingusing plasma. In addition, even when fine particles which tend to gatherat a depressed portion are generated, the fine particles can be washed,and yield can be expected to increase significantly. That is to say, theproblems of dust and fine particles in manufacturing steps can besolved. Further, the round corner of the wire allows electricalconduction. In addition, dust in multiple parallel wires can be washedeffectively.

Embodiment Mode 10

By using a display device formed by the invention, a television devicecan be completed. FIG. 26 is a block diagram showing a major structureof a television device (in this embodiment mode, an EL televisiondevice). In a display panel, there are a case where only a pixel portionis formed in such a structure as shown in FIG. 20A and a scan linedriver circuit and a signal line driver circuit are mounted by a TABmethod as shown in FIG. 21B, a case where they are mounted by a COGmethod as shown in FIG. 21A, a case where TFTs are formed of SAS asshown in FIG. 20B, the pixel portion and the scan line driver circuitare integrated over the substrate, and the signal line driver circuit ismounted as a driver IC separately, and a case where the pixel portion,the signal line driver circuit, and the scan line driver circuit areintegrated over the substrate as shown in FIG. 20C. The display panelmay have any of the aforementioned modes.

As another configuration of an external circuit, on an input side ofvideo signals, a video signal amplifier circuit 705 which amplifies avideo signal among signals received by a tuner 704, a video signalprocessing circuit 706 which converts a signal outputted from the videosignal amplifier circuit 705 into a color signal corresponding to eachof red, green, and blue, a control circuit 707 which converts the videosignal into an input specification of the driver IC, and the like areincluded. The control circuit 707 outputs signals to the scan line sideand the signal line side. In the case of digital driving, a signaldividing circuit 708 is provided on the signal line side so that inputdigital signals are divided into m pieces to be supplied.

Among the signals received by the tuner 704, audio signals aretransmitted to an audio signal amplifier circuit 709 of which output issupplied to a speaker 713 through an audio signal processing circuit710. The control circuit 711 receives control data such as a receivingstation (receiving frequency) and volume from an input portion 712 andtransmits signals to the tuner 704 and the audio signal processingcircuit 710.

By incorporating a display module in a housing as shown in FIGS. 27A and27B, a television device can be completed. A display panel in whichcomponents up to an FPC are set is generally also called an EL displaymodule. Therefore, by using the EL display module, the EL televisiondevice can be completed. A main screen 2003 is formed by the displaymodule, and as other attachment systems, a speaker portion 2009, anoperating switch, and the like are provided. In this manner, atelevision device can be completed by the invention.

By using a retardation film or a polarizing plate, reflected light oflight incident from outside may be blocked. In the case of a topemission type display device, an insulating layer as a partition may becolored to be used as a black matrix. The partition can be formed by adroplet discharge method or the like as well, using pigment-based blackresin or a resin material such as polyimide mixed with carbon black orthe like, or a stacked-layer of these. A partition may be formed bydischarging different materials in the same region a plurality of timesby a droplet discharge method. As the retardation film, a quarter waveplate and a half wave plate may be used and may be designed to be ableto control light. As the structure, the light emitting element, thesealing substrate (sealant), the retardation film (quarter wave plate),the retardation film (half wave plate), and the polarizing plate aresequentially laminated over a TFT element substrate, in which lightemitted from the light emitting element is transmitted therethrough andemitted outside from a polarizing plate side. The retardation films orpolarizing plate may be provided on a side where light is emittedoutside or may be provided on both sides in the case of a dual emissiontype display device in which light is emitted from the both surfaces. Inaddition, an anti-reflective film may be provided outside of thepolarizing plate. Accordingly, an image with higher resolution andprecision can be displayed.

As shown in FIG. 27A, a display panel 2002 using a display element isincorporated in a housing 2001. By connecting to a communication networkin a wired or wireless manner through a modem 2004, one way (transmitterto receiver) or two-way (between transmitter and receiver or betweenreceivers) data communication is possible as well as general televisionbroadcast can be received by a receiver 2005. The television device canbe operated by using a switch incorporated in the housing or a separateremote control operator 2006. The remote control operator may beprovided with a display portion 2007 which displays outputted data.

In the television device, a sub screen 2008 may be formed of a seconddisplay panel in addition to the main screen 2003, which has a structureto display a channel, volume, or the like. In this structure, the mainscreen 2003 may be formed of an EL display panel with a superior viewingangle while the sub screen may be formed of a liquid crystal displaypanel which can perform display with low power consumption. To givepriority to low power consumption, the main screen 2003 may be formed ofa liquid crystal display panel and the sub screen may be formed of an ELdisplay panel so as to be capable of blinking. By using the invention, ahighly reliable display device can be manufactured even by using a largesubstrate with a lot of TFTs and electronic components.

FIG. 27B is a television device having a large display portion in a sizeof, for example, 20 to 80 inches, including a housing 2010, a keyboardportion 2012 as an operating portion, a display portion 2011, a speakerportion 2013, and the like. The invention is applied to manufacturing ofthe display portion 2011. The display portion shown in FIG. 27B isformed of a substance which can be curved; therefore, the televisiondevice has the curved display portion. In this manner, the shape of thedisplay portion can be freely designed; therefore, a television devicein a desired shape can be manufactured.

By the invention, a display device can be manufactured throughsimplified steps; therefore, cost can be reduced as well. As a result, atelevision device manufactured by the invention can be manufactured atlow cost even with a large display portion. Thus, a television devicewith high functionality and high reliability can be manufactured at highyield.

It is needless to say that the invention is not limited to a televisiondevice and the invention can be used for various applications as a largedisplay medium such as an information display board at train stations,airports, and the like, and an advertisement board on street as well asa monitor of a personal computer.

Embodiment Mode 11

This embodiment mode is described with reference to FIGS. 28A and 28B.This embodiment mode shows an example of a module using a panelincluding a display device manufactured in Embodiment Modes 1 to 9.

A module of an information terminal shown in FIG. 28A includes a printedwiring board 986 over which a controller 901, a central processing unit(CPU) 902, a memory 911, a power source circuit 903, an audio processingcircuit 929, a transmission/reception circuit 904, and other elementssuch as a resistor, a buffer, and a capacitor are mounted. In addition,a panel 900 is connected to the printed wiring board 986 through aflexible wiring circuit (FPC) 908.

The panel 900 is provided with a pixel portion 905 having a lightemitting element in each pixel, a first scan line driver circuit 906 a,a second scan line driver circuit 906 b which selects a pixel includedin the pixel portion 905, and a signal line driver circuit 907 whichsupplies a video signal to the selected pixel.

Various control signals are inputted and outputted through an interface(I/F) portion 909 provided on the printed wiring board 986. An antennaport 910 for transmitting and receiving signals to/from an antenna isprovided on the printed wiring board 986.

It is to be noted in this embodiment mode that the printed wiring board986 is connected to the panel 900 through the FPC 908; however, theinvention is not limited to this structure. The controller 901, theaudio processing circuit 929, the memory 911, the CPU 902, or the powersource circuit 903 may be directly mounted on the panel 900 by a COG(Chip on Glass) method. Moreover, various elements such as a capacitorand a buffer provided on the printed wiring board 986 prevent a noise ina power source voltage or a signal and a rounded rise of a signal.

FIG. 28B is a block diagram of the module shown in FIG. 28A. A module999 includes a VRAM 932, a DRAM 925, a flash memory 926, and the like asthe memory 911. The VRAM 932 stores image data displayed by a panel, theDRAM 925 stores image data or audio data, and the flash memory storesvarious programs.

The power source circuit 903 generates a power source voltage applied tothe panel 900, the controller 901, the CPU 902, the audio processingcircuit 929, the memory 911, and the transmission/reception circuit 931.Moreover, depending on the specifications of the panel, a current sourceis provided in the power source circuit 903 in some cases.

The CPU 902 includes a control signal generating circuit 920, a decoder921, a register 922, an arithmetic circuit 923, a RAM 924, an interface935 for the CPU, and the like. Various signals inputted to the CPU 902through the interface 935 are inputted to the arithmetic circuit 923,the decoder 921, and the like after being held in the register 922 once.The arithmetic circuit 923 operates based on the inputted signal andspecifies an address to send various instructions. On the other hand, asignal inputted to the decoder 921 is decoded and inputted to thecontrol signal generating circuit 920. The control signal generatingcircuit 920 generates a signal containing various instructions based onthe inputted signal and sends it to the address specified by thearithmetic circuit 923, which are specifically the memory 911, thetransmission/reception circuit 931, the audio processing circuit 929,the controller 901, and the like.

The memory 911, the transmission/reception circuit 931, the audioprocessing circuit 929, and the controller 901 operate in accordancewith respective transmitted instructions. The operations are brieflydescribed below.

The signal inputted from an input unit 930 is transmitted to the CPU 902mounted on the printed wiring board 986 through the interface 909. Thecontrol signal generating circuit 920 converts the image data stored inthe VRAM 932 into a predetermined format in accordance with the signaltransmitted from the input unit 930 such as a pointing device and akeyboard, and then transmits it to the controller 901.

The controller 901 processes a signal containing image data transmittedfrom the CPU 902 in accordance with the specifications of the panel andsupplies it to the panel 900. The controller 901 generates and sends aHsync signal, a Vsync signal, a clock signal CLK, an alternating voltage(AC Cont), and a switching signal L/R to the panel 900 based on thepower source voltage inputted from the power source circuit 903 andvarious signals inputted from the CPU 902.

In the transmission/reception circuit 904, a signal transmitted andreceived as an electric wave by the antenna 933 is processed. Inspecific, high frequency circuits such as an isolator, a band pathfilter, a VCO (Voltage Controlled Oscillator), an LPF (Low Pass Filter),coupler, and balan are included. Among the signals transmitted andreceived by the transmission/reception circuit 904, signals containingaudio data are transmitted to an audio processing circuit 929 inaccordance with an instruction transmitted from the CPU 902.

The signals containing audio data transmitted in accordance with theinstruction from the CPU 902 are demodulated into audio signals in theaudio processing circuit 929 and transmitted to a speaker 928. The audiosignal transmitted from a microphone 927 is modulated in the audioprocessing circuit 929 and transmitted to the transmission/receptioncircuit 904 in accordance with the instruction from the CPU 902.

The controller 901, the CPU 902, the power source circuit 903, the audioprocessing circuit 929, and the memory 911 can be incorporated as apackage of this embodiment mode. This embodiment mode can be applied toany circuit besides high frequency circuits such as an isolator, a bandpath filter, a VCO (Voltage Controlled Oscillator), an LPF (Low PassFilter), coupler, and balan.

Embodiment Mode 12

A configuration of a semiconductor device of this embodiment mode isdescribed with reference to FIG. 29. As shown in FIG. 29, asemiconductor device 28 of the invention has a function to communicatedata wirelessly, and includes a power source circuit 11, a clockgenerating circuit 12, a data demodulation/modulation circuit 13, acontrol circuit 14 which controls other circuits, an interface circuit15, a memory circuit 16, a data bus 17, an antenna (antenna coil) 18, asensor 26, and a sensor circuit 27.

The power source circuit 11 generates various power sources to besupplied to each circuit in the semiconductor device 28 based onalternating signals inputted from the antenna 18. The clock generatingcircuit 12 generates various clock signals to be supplied to eachcircuit in the semiconductor device 28 based on alternating signalsinputted from the antenna 18. The data demodulation/modulation circuit13 has a function to demodulate/modulate data to communicate with thereader/writer 19. The control circuit 14 has a function to control thememory circuit 16. The antenna 18 has a function to transmit and receiveelectromagnetic waves or electric waves. The reader/writer 9 controls aprocess related to communication, control, and data of the semiconductordevice. It is to be noted that the semiconductor device is not limitedto have the aforementioned configuration. For example, other elementssuch as a limiter circuit of a power source voltage or hardwarededicated for cipher processing may be additionally provided.

The memory circuit 16 features that a memory element in which an organiccompound layer or a phase change layer is sandwiched between a pair ofconductive layers is included. The memory circuit 16 may have only amemory element in which an organic compound layer or a phase changelayer is sandwiched between a pair of conductive layers or may have amemory circuit with another configuration in addition. The memorycircuit with another configuration corresponds to one or a pluralityselected from, for example, a DRAM, an SRAM, a FeRAM, a mask ROM, aPROM, an EPROM, an EEPROM, and a flash memory.

The sensor 26 is formed of a semiconductor element such as a resistor, acapacitive coupling element, an inductive coupling element, aphoto-electromotive element, a photoelectric converting element, athermo-electromotive element, a transistor, a thermistor, and a diode.The sensor circuit 27 detects a change in impedance, reactance,inductance, voltage, or current and carries out analog/digitalconversion (A/D conversion) and outputs a signal to the control circuit14.

Embodiment Mode 13

This embodiment mode is described with reference to FIG. 25. FIG. 25shows one aspect of a portable phone (mobile phone) including the modulemanufactured in Embodiment Mode 11, which operates wirelessly and can becarried. Moreover, a semiconductor device using the invention isincorporated in the portable phone. The panel 900 is detachablyincorporated in a housing 981 so as to be easily combined with a module999. The housing 981 can be appropriately changed in shape and size inaccordance with an electronic device incorporated therein.

The housing 981 in which the panel 900 is fixed is fit in the printedwiring board 986 and set up as a module. A plurality of semiconductordevices which are packaged are incorporated in the printed wiring board986, for one of which a semiconductor device of the invention can beused. The plurality of semiconductor devices incorporated in the printedwiring board 986 have any function of a controller, a central processingunit (CPU), a memory, a power source circuit, and other elements such asa resistor, a buffer, and a capacitor. Moreover, an audio processingcircuit including a microphone 994 and a speaker 995 and a signalprocessing circuit 993 such as a transmission/reception circuit areprovided. The panel 900 is connected to the printed wiring board 986through the FPC 908.

The module 999, the housing 981, the printed wiring board 986, an inputunit 998, and a battery 997 are stored in a housing 996. The pixelportion of the panel 900 is arranged so that it can be seen through awindow formed in the housing 996. As a semiconductor device of theinvention can be highly integrated easily, an electronic device using asemiconductor device having a large capacitance memory circuit can beprovided. Further, a highly reliable electronic device can bemanufactured at high productivity.

The housing 996 shown in FIG. 25 shows an exterior shape of a portablephone as an example. However, an electronic device of this embodimentmode could change to have various aspects in accordance with functionsand applications. In the following embodiment mode, an example of theaspects is described.

Embodiment Mode 14

By using the invention, various display devices can be manufactured.That is, the invention can be applied to various electronic devicesincorporating the display device in a display portion.

Such electronic devices include a camera such as a video camera and adigital camera, a projector, a head mounted display (goggle typedisplay), a car navigation system, a car stereo, a personal computer, agame machine, a portable information terminal (mobile computer, mobilephone, electronic book, or the like), an image reproducing deviceprovided with a recording medium (specifically a device which reproducesa recording medium such as a DVD (Digital Versatile Disc) and has adisplay capable of displaying the reproduced image), and the like.Examples of these are shown in FIGS. 32A to 32D.

FIG. 32A illustrates a computer including a main body 2101, a housing2102, a display portion 2103, a keyboard 2104, an external connectingport 2105, a pointing mouse 2106, and the like. In this computer, thedisplay portion 2103 has a structure of the aforementioned embodimentmode. As a result, an aperture ratio of the display portion 2103 of thecomputer can be improved. Further, a highly reliable computer whichdisplays a high quality image can be provided.

FIG. 32B illustrates an image reproducing device provided with arecording medium (specifically a DVD reproducing device), including amain body 2201, a housing 2202, a display portion A 2203, a displayportion B 2204, a recording medium (DVD or the like) reading portion2205, an operating key 2206, a speaker portion 2207, and the like. Thedisplay portion 2203 A mainly displays image data while the displayportion B 2204 mainly displays text data. In the image reproducingdevice provided with a recording medium, the display portion A 2203 andthe display portion B 2204 have the structures of the aforementionedembodiment mode. As a result, an aperture ratio of each of the displayportion A 2203 and the display portion B 2204 of the image reproducingdevice provided with a recording medium can be improved. Further, ahighly reliable image reproducing device provided with a recordingmedium, which displays a high quality image, can be provided.

FIG. 32C illustrates a portable phone including a main body 2301, anaudio output portion 2302, an audio input portion 2303, a displayportion 2304, operating switches 2305, an antenna 2306, and the like. Inthis portable phone, the display portion 2304 has the structure of theaforementioned embodiment mode. As a result, an aperture ratio of thedisplay portion 2304 of the portable phone can be improved. Further, ahighly reliable portable phone which displays a high quality image canbe provided.

FIG. 32D illustrates a video camera including a main body 2401, adisplay portion 2402, a housing 2403, an external connecting port 2404,a remote control receiving portion 2405, an image receiving portion2406, a battery 2407, an audio input portion 2408, an eyepiece portion2409, operating keys 2410, and the like. In this video camera, thedisplay portion 2402 has the structure of the aforementioned embodimentmode. As a result, an aperture ratio of the display portion 2402 of thevideo camera can be improved. Further, a highly reliable video camerawhich displays a high quality image can be provided. This embodimentmode can be freely implemented in combination with the aforementionedembodiment modes.

Embodiment Mode 15

By the invention, a semiconductor device functioning as a processor chip(also referred to as a wireless chip, a wireless processor, a wirelessmemory, or a wireless tag) can be formed. The semiconductor device ofthe invention is used for various purposes. The semiconductor device canbe used for, for example, bills, coins, securities, certificates, bearerbonds, packages, documents, recording media, personal belongings,vehicles, food, clothing, health products, commodities, chemicals,electronic appliances, and the like.

Bills and coins are money that circulate in the market and include onesvalid in a certain area (cash voucher), memorial coins, and the like.Securities include checks, certificates, promissory notes, and the like,and can be provided with a processor chip 90 (see FIG. 30A).Certificates include driver's licenses, certificates of residence, andthe like, and can be provided with a processor chip 91 (see FIG. 30B).Personal belongings include bags, glasses, and the like, and can beprovided with a processor chip 97 (see FIG. 30C). Bearer bonds includestamps, rice coupons, various gift certificates, and the like. Packagesinclude wrapping paper for food containers and the like, plasticbottles, and the like, and can be provided with a processor chip 93 (seeFIG. 30D). Books include hardbacks, paperbacks, and the like, and can beprovided with a processor chip 94 (see FIG. 30E). Recording mediainclude DVD software, video tapes, and the like, and can be providedwith a processor chip 95 (see FIG. 30F). Vehicles include wheeledvehicles such as bicycles, ships, and the like, and can be provided witha processor chip 96 (see FIG. 30G). Food includes food articles, drink,and the like. Clothing include clothes, footwear, and the like. Healthproducts include medical instruments, health instruments, and the like.Commodities include furniture, lighting equipment, and the like.Chemicals includes medical products, pesticides, and the like.Electronic devices include liquid crystal display devices, EL displaydevices, television devices (TV sets and flat-screen TV sets), portablephones, and the like.

The semiconductor device of the invention is fixed to a product by beingmounted on a printed board, attached to the surface of the product, orembedded in the product. For example, the semiconductor device may beembedded in the paper of a book, or an organic resin of a package. Sincethe semiconductor device of the invention is small, thin, andlightweight, it can be fixed to a product without detracting from thedesign of the product itself. In addition, when provided with thesemiconductor device of the invention, bills, coins, securities, bearerbonds, certificates, and the like can have an authentication function.The use of the authentication function prevents forgery. When thesemiconductor device of the invention is incorporated in containers forpackages, recording media, personal belongings, foods, commodities,clothing, electronic apparatuses, and the like, systems such asinspection systems can be performed more efficiently.

An example of capable of being applied to product management anddistribution system is described with reference to FIGS. 31A and 31B.This embodiment mode shows an example of incorporating a processor chipin a product. As shown in FIG. 31A, a processor chip 3402 is mounted ona beer bottle 3400 using a label 3401.

The processor chip 3402 stores basic data such as a manufacturing date,a manufacturing area, and ingredients. Such basic data is not requiredto be rewritten, thus it may be stored in a non-rewritable memory suchas a mask ROM and a memory element of the invention. The basic data suchas a manufacturing date, a manufacturing area, and ingredients isinformation that consumers may want to correctly obtain when purchasinga product. When such information is stored in a non-rewritable memoryelement, falsification of data and the like can be prevented, and thusaccurate information with high reliability can be transmitted to theconsumers. The processor chip 3402 also stores individual data such as adelivery address and a delivery date of each beer bottle. For example,as shown in FIG. 31B, when the beer bottle 3400 moving on a conveyorbelt 3412 passes a writer device 3413, each delivery address anddelivery date can be stored in the processor chip 3402. Such individualdata may be stored in a rewritable and erasable memory such as anEEPROM.

A system is preferably configured such that when data on a purchasedproduct is transmitted from a delivery destination to a distributionmanagement center via a network, the delivery address and date arecalculated based on the product data by a writer device, a personalcomputer for controlling the writer device, or the like, and then storedin the processor chip.

Since the bottles are delivered per case, a processor chip may beincorporated in each case or every several cases to store individualdata.

When the processor chip is incorporated in such products that may storea plurality of delivery addresses, the time required for manual datainput can be reduced, resulting in reduced input errors. In addition, itis possible to lower labor costs that are the most costly expenses inthe distribution management. Thus, incorporation of the processor chipallows the distribution management to be performed with few errors atlow cost.

Additional data such as food to go with beer and a recipe with beer maybe stored at the delivery destination. As a result, the food and thelike can be promoted and consumers' willingness to buy can be increased.Such additional data may be stored in a rewritable and erasable memorysuch as an EEPROM. In this manner, incorporation of the processor chipincreases the amount of information given to consumers; thus they canpurchase products at ease.

Embodiment Mode 16

In this embodiment mode, other structures which can be applied to alight emitting element of the invention are described with reference toFIGS. 34A to 35C.

A light emitting element which utilizes electroluminescence iscategorized depending on a light emitting material: an organic compoundor an inorganic compound. In general, the former is called an organic ELelement while the latter is called an inorganic EL element.

The inorganic EL element is categorized into a dispersion type inorganicEL element and a thin film inorganic EL element depending on the elementstructure. The former has an electroluminescent layer in which particlesof light emitting material are dispersed in a binder while the latterhas an electroluminescent layer formed of a thin film of a lightemitting material. However, they are common in that an electronaccelerated in a high electronic field is required. As a light emissionmechanism, there are a donor-acceptor recombination type light emissionwhich utilizes a donor level and an acceptor level and a localized typelight emission which utilizes inner-shell electron transition of metalions. In general, a dispersion type inorganic EL element employs adonor-acceptor recombination type light emission while a thin film typeinorganic EL element employs localized light emission in many cases.

A light emitting material which can be used in the invention is formedof a host material and an impurity element as a light emission center.By changing the impurity element to be contained, light emission ofvarious colors can be obtained. As a manufacturing method of a lightemitting material, various methods such as a solid phase method and aliquid phase method (coprecipitation method) can be used. In addition, aliquid phase method such as a spray pyrolysis method, a metathesismethod, a method by pyrolysis decomposition reaction of precursor, areverse micelle method, a combination method of the aforementionedmethod and high temperature baking, a freeze drying method, or the likecan be used.

In the solid phase method, a host material and an impurity element or acompound containing an impurity element are weighed, mixed in a mortar,and heated and baked in an electric furnace so as to react, thereby theimpurity element is contained in the host material. The bakingtemperature is preferably 700 to 1500° C. When the temperature is toolow, the solid phase reaction does not proceed while when thetemperature is too high, the host material is decomposed. It is to benoted that baking may be carried out in a powder state; however, apellet state is preferable. A relatively high temperature is requiredfor baking; however, this method being simple and favorable inproductivity is suitable for mass production.

The liquid phase method (coprecipitation method) is a method to react ahost material or a compound containing a host material and an impurityelement or a compound containing an impurity element in a solution,dried, and then baked. The particles of the light emitting material areevenly distributed; therefore, the reaction proceeds even with smallparticles at a low baking temperature.

As a host material used for the light emitting material, sulfide, oxide,and nitride can be used. As sulfide, for example, zinc sulfide (ZnS),cadmium sulfide (CdS), calcium sulfide (CaS), yttrium sulfide (Y₂S₃),gallium sulfide (Ga₂S₃), strontium sulfide (SrS), barium sulfide (BaS)or the like can be used. As oxide, for example, zinc oxide (ZnO),yttrium oxide (Y₂O₃), or the like can be used. As nitride, for example,aluminum nitride (AlN), gallium nitride (GaN), indium nitride (InN), orthe like can be used. Furthermore, zinc selenide (ZnSe), zinc telluride(ZnTe) or the like can also be used and a mixed crystal of ternarycompound system such as calcium gallium-sulfide (CaGa₂S₄), strontiumgallium sulfide (SrGa₂S₄), or barium-gallium sulfide (BaGa₂S₄) may beused as well.

As the light emission center of the localized type light emission,manganese (Mn), copper (Cu), samarium (Sm), terbium (Tb), erbium (Er),thulium (Tm), europium (Eu), cerium (Ce), praseodymium (Pr), or the likecan be used. In addition, as charge compensation, halogen element suchas fluorine (F) and chlorine (Cl) may be added.

On the other hand, as a light emission center of the donor-acceptorrecombination type light emission, a light emitting material containinga first impurity element which forms a donor level and a second impurityelement which forms an acceptor level can be used. As the first impurityelement, for example, fluorine (F), chlorine (Cl), aluminum (Al), or thelike can be used. As the second impurity element, for example, copper(Cu), silver (Ag), or the like can be used.

In the case of synthesizing the light emitting material of thedonor-acceptor recombination type light emission by the solid phasemethod, a host material, a first impurity element or a compoundcontaining the first impurity element, and a second impurity element ora compound containing the second impurity element are each weighed andmixed in a mortar, and then heated and baked in an electronic furnace.As the host material, the aforementioned host material can be used. Asthe first impurity element or the compound containing the first impurityelement, for example, fluorine (F), chlorine (Cl), aluminum sulfide(Al₂S₃), and the like can be used. As the second impurity element or acompound containing the second impurity element, for example, copper(Cu), silver (Ag), copper sulfide (Cu₂S), silver sulfide (Ag₂S), and thelike can be used. The baking temperature is preferably 700 to 1500° C.When the temperature is too low, the solid phase reaction does notproceed while when the temperature is too high, the host material isdecomposed. It is to be noted that baking may be carried out in a powderstate; however, a pellet state is preferable.

As an impurity element used in the case of utilizing the solid phasereaction, a compound formed of the first impurity element and the secondimpurity element may be used in combination. In this case, the impurityelement is easily dispersed which facilitates the solid phase reaction.Therefore, an even light emitting material can be obtained. Furthermore,as no redundant impurity elements are included, a highly pure lightemitting material can be obtained. As a compound formed of the firstimpurity element and the second impurity element, for example, copperchloride (CuCl), silver chloride (AgCl), or the like can be used.

It is to be noted that the concentration of these impurity elements maybe 0.01 to 10 atom %, or preferably 0.05 to 5 atom % with respect to thehost material.

In the case of a thin film type inorganic EL element, theelectroluminescent layer contains the aforementioned light emittingmaterial and can be formed by a resistance heating vapor depositionmethod, a vacuum vapor deposition method such as electron beamevaporation (EB deposition) method, a physical vapor deposition method(PVD) such as a sputtering method, an organic metal CVD method, achemical vapor deposition method (CVD) such as hydride transfer lowpressure CVD method, an atomic layer epitaxy method (ALE), or the like.

FIGS. 34A to 34C show examples of thin film type inorganic EL elementswhich can be used as light emitting elements. In FIGS. 34A to 34C, eachlight emitting element includes a first electrode layer 50, anelectroluminescent layer 51, and a second electrode layer 53.

Each light emitting element shown in FIGS. 34B and 34C has a structurewhere an insulating layer is provided between an electrode layer and anelectroluminescent layer in the light emitting element shown in FIG.34A. The light emitting element shown in FIG. 34B includes an insulatinglayer 54 between the first electrode layer 50 and the electroluminescentlayer 52. The light emitting element shown in FIG. 34C includes aninsulating layer 54 a between the first electrode layer 50 and theelectroluminescent layer 52 and an insulating layer 54 b between thesecond electrode layer 53 and the electroluminescent layer 52. In thismanner, an insulating layer may be provided between one or both of pairsof electrode layers sandwiching an electroluminescent layer. Theinsulating layer may be formed of a single layer or a plurality oflayers.

Further, the insulating layer 54 is provided so as to contact the firstelectrode layer 50; however, the insulating layer 54 may be provided soas to contact the second electrode layer 53 by reversing the order ofthe insulating layer and the electroluminescent layer.

In the case of a dispersion type inorganic EL element, anelectroluminescent layer in a film state is formed by dispersing a lightemitting material in particles in binder. In the case where particles ina desired shape cannot be obtained sufficiently depending on amanufacturing method of a light emitting material, the particles may beprocessed by crushing in a mortar or the like. The binder is a substancefor fixing the light emitting material in particles in a dispersed stateand holding them in a shape as an electroluminescent layer. The lightemitting material is evenly dispersed in the electroluminescent layerand fixed by the binder.

In the case of a dispersion type inorganic EL element, theelectroluminescent layer may be formed by a droplet discharge method bywhich an electroluminescent layer can be selectively formed, a printingmethod (such as screen printing or offset printing), a coating methodsuch as a spin coating method, a dipping method, a dispenser method, orthe like. The thickness it not particularly limited; however, it ispreferably 10 to 1000 nm. Further, it is preferable that the ratio ofthe light emitting material is 50 to 80 wt % in the electroluminescentlayer containing a light emitting material and binder.

FIGS. 35A to 35C show examples of a dispersion type inorganic EL elementwhich can be used as a light emitting element. The light emittingelement shown in FIG. 35A has a stacked-layer structure of a firstelectrode layer 60, an electroluminescent layer 62, and a secondelectrode layer 63. The electroluminescent layer 62 contains a lightemitting material 61 held by the binder.

An insulating material can be used as binder in this embodiment mode. Amixed material of an organic material and an inorganic material may alsobe used. As the organic insulating material, a polymer material having arelatively high dielectric constant such as cyanoethyl cellulose-basedresin, resin such as polyethylen, polypropylene, polystyrenic resin,silicone resin, epoxy resin, and vinylidene fluoride can be used.Moreover, heat resistant high molecular such as aromatic polyamide,polybenzimidazole, or siloxane resin may be used. A siloxane resinincludes a Si—O—Si bond. Siloxane has a skeleton formed by the bond ofsilicon (Si) and oxygen (O), in which an organic group containing atleast hydrogen (such as an alkyl group and aromatic hydrocarbon) isincluded as a substituent. Alternatively, a fluoro group may be used asthe substituent. Further alternatively, a fluoro group and an organicgroup containing at least hydrogen may be used as the substituent.Further, vinyl resin such as polyvinyl alcohol and polyvinyl butyral, aresin material such as phenol resin, novolac resin, acrylic resin,melamine resin, urethane resin, and oxazole resin (polybenzoxazole) maybe used. A dielectric constant can be controlled by mixing microparticles having a high dielectric constant such as barium titanate(BaTiO₃) and strontium titanate (SrTiO₃) in the aforementioned resin.

As an inorganic insulating material included in binder, a materialselected from silicon oxide (SiOx), silicon nitride (SiNx), siliconincluding oxygen and nitrogen, aluminum nitride (AlN), aluminumincluding oxygen and nitrogen, aluminum oxide (Al₂O₃), titanium oxide(TiO₂), BaTiO₃, SrTiO₃, lead titanate (PbTiO₃), potassium niobate(KNbO₃), lead niobate (PbNbO₃), tantalum oxide (Ta₂O₅), barium tantalate(BaTa₂O₆), lithium tantalite (LiTaO₃), yttrium oxide (Y₂O₃), zirconia(ZrO₂), and other substances containing an inorganic insulating materialcan be used. When an organic material contains an inorganic materialhaving a high dielectric constant (by adding or the like), a dielectricconstant of the electroluminescent layer formed of a light emittingmaterial and binder can be more controlled, thereby the dielectricconstant can be larger. By using a mixed layer of an inorganic materialand an organic material for the binder so as to obtain a high dielectricconstant, a large charge can be induced in the light emitting material.

A light emitting material is dispersed in a solution containing binderin the manufacturing steps. As a solvent of a solution containing binderwhich can be used in this embodiment mode, a solvent which enables thebinder material to be dissolved and to manufacture a solution with asuitable viscosity for a desired whickness and a method for forming anelectroluminescent layer (various wet processes) may be appropriatelyselected. An organic solvent or the like can be used, for example,propylene glycol monomethyl ether, propylene glycol monomethyl etheracetate (also called PGMEA), 3-methoxy-3-methyl-1-butanol (also calledMMB) and the like can be used in the case of using siloxane resin as thebinder.

Each of the light emitting elements shown in FIGS. 35B and 35C has astructure where an insulating layer is provided between an electrodelayer and an electroluminescent layer in the light emitting element ofFIG. 35A. The light emitting element shown in FIG. 35B has an insulatinglayer 64 between a first electrode layer 60 and the electroluminescentlayer 62. The light emitting element shown in FIG. 35C has an insulatinglayer 64 a between the first electrode layer 60 and theelectroluminescent layer 62, and an insulating layer 64 b between asecond electrode layer 63 and the electroluminescent layer 62. In thismanner, an insulating layer may be provided between one or both of pairsof electrode layers sandwiching an electroluminescent layer. Theinsulating layer may be formed of a single layer or a plurality oflayers.

In FIG. 35B, the insulating layer 64 is provided so as to contact thefirst electrode layer 60; however, the insulating layer 64 may beprovided so as to contact the second electrode layer 63 by reversing theorder of the insulating layer and the electroluminescent layer.

An insulating layer such as the insulating layer 54 in each of FIGS. 34Ato 34C and the insulating layer 64 in FIG. 35 is not particularlylimited; however, it preferably has a high insulating property, a densefilm quality, and further a high dielectric constant. For example,silicon oxide (SiO₂), yttrium oxide (Y₂O₃), titanium oxide (TiO₂),aluminum oxide (Al₂O₃), hafnium oxide (HfO₂), tantalum oxide (Ta₂O₅),barium titanate (BaTiO₃), strontium titanate (SrTiO₃), lead titanate(PbTiO₃), silicon nitride (Si₃N₄), zirconia (ZrO₂), and the like, amixed film or a stacked-layer of two or more kinds of the aforementionedsubstances can be used. These insulating films can be formed by asputtering method, a vapor deposition method, a CVD method, or the like.Moreover, the insulating layer may be formed by dispersing particles ofthese insulating materials in a binder. The binder material may beformed of a similar material and method to the binder contained in theelectroluminescent layer. The film thickness is not particularlylimited; however, it is preferably 10 to 1000 nm.

In the light emitting element described in this embodiment mode, lightis emitted by applying a voltage between a pair of electrode layerswhich sandwich an electroluminescent layer. An operation is possiblewith either a DC drive or an AC drive.

By using the invention, a thin film transistor which drives the lightemitting element described in this embodiment mode can be manufacturedby a simplified method with high reliability. Therefore, a highlyreliable display device can be manufactured through simplified steps. Asa result, a display device with high resolution and high image qualitycan be manufactured at low cost and high yield.

What is claimed is:
 1. A method for manufacturing a semiconductor devicecomprising: forming a semiconductor layer over a substrate; forming afirst insulating layer over the semiconductor layer; forming a firstconductive layer over the first insulating layer; forming a secondconductive layer over and in contact with the first conductive layer;adding an impurity into the semiconductor layer to form a non-impurityadded region at one end of the semiconductor layer, a first impurityregion, and a second impurity region at the other end of thesemiconductor layer; and forming a second insulating layer over thesecond conductive layer and in direct contact with a portion of a topsurface of the first conductive layer, wherein a width of the firstconductive layer is larger than a width of the second conductive layer.2. The method for manufacturing a semiconductor device according toclaim 1, wherein the impurity is an n-type impurity.
 3. The method formanufacturing a semiconductor device according to claim 1, wherein animpurity concentration of the second impurity region is higher than animpurity concentration of the first impurity region.
 4. The method formanufacturing a semiconductor device according to claim 1, furthercomprising a step of forming a wiring layer in direct contact with thesecond impurity region.
 5. A method for manufacturing a semiconductordevice comprising: forming a semiconductor layer over a substrate;forming a first insulating layer over the semiconductor layer; forming afirst conductive layer over the first insulating layer; forming a secondconductive layer over and in contact with the first conductive layer;adding an impurity into the semiconductor layer to form a non-impurityadded region at one end of the semiconductor layer, a first impurityregion, and a second impurity region at the other end of thesemiconductor layer; and forming a second insulating layer over thesecond conductive layer and in direct contact with a portion of a topsurface of the first conductive layer, wherein a width of the firstimpurity region is larger than a width of the non-impurity added region,and wherein a width of the first conductive layer is larger than a widthof the second conductive layer.
 6. The method for manufacturing asemiconductor device according to claim 5, wherein the impurity is ann-type impurity.
 7. The method for manufacturing a semiconductor deviceaccording to claim 5, wherein an impurity concentration of the secondimpurity region is higher than an impurity concentration of the firstimpurity region.
 8. The method for manufacturing a semiconductor deviceaccording to claim 5, further comprising a step of forming a wiringlayer in direct contact with the second impurity region.
 9. A method formanufacturing a semiconductor device comprising: forming a semiconductorlayer over a substrate; forming a first insulating layer over thesemiconductor layer; forming a first conductive layer over the firstinsulating layer; forming a second conductive layer over and in contactwith the first conductive layer; adding an impurity into thesemiconductor layer to form a non-impurity added region at one end ofthe semiconductor layer, a first impurity region, and a second impurityregion at the other end of the semiconductor layer; and forming secondinsulating layer over the second conductive layer and in direct contactwith a portion of a top surface of the first conductive layer, wherein awidth of the first impurity region is larger than a width of the secondimpurity region, and wherein a width of the first conductive layer islarger than a width of the second conductive layer.
 10. The method formanufacturing a semiconductor device according to claim 9, wherein theimpurity is an n-type impurity.
 11. The method for manufacturing asemiconductor device according to claim 9, wherein an impurityconcentration of the second impurity region is higher than an impurityconcentration of the first impurity region.
 12. The method formanufacturing a semiconductor device according to claim 9, furthercomprising a step of forming a wiring layer in direct contact with thesecond impurity region.